We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
Updated: 2026-09-17 · 7 min read · Independent comparison
If you want a desktop headphone amplifier and DAC that can also double as a Bluetooth hub for a full-size wired setup, choose FiiO K9; if you need true wireless in-ear earbuds with sound personalization for life on the move, choose Noble Audio FoKus Rex5. These two products sit in completely different categories, so the real question isn't which one is "better" — it's which one actually matches how you listen.
• FiiO K9 — biggest strength: a serious desktop DAC/amp chain built around dual ES9068AS DACs and a THX AAA 788+ amplifier, with isolated digital and analog power and a genuinely wide set of outputs.
• FiiO K9 — biggest trade-off: it's a 2660 g desktop unit that needs a power connection. It stays put on a desk, and it has no built-in battery for portable use.
• Noble Audio FoKus Rex5 — biggest strength: true wireless freedom with a personalized-sound feature, a built-in microphone and a charging case that carries a 500 mAh battery.
• Noble Audio FoKus Rex5 — biggest trade-off: it's an in-ear, sound-isolation design with no wired jack, so it won't drive power-hungry full-size headphones or feed a speaker system.
• Who each pick is for: the FiiO K9 is for someone building a home listening station around wired headphones; the FoKus Rex5 is for someone who wants premium-feeling earbuds for commuting, workouts and calls.
The K9 is a desktop component, and it's honest about that. Two ES9068AS DAC chips split the left and right channels, and the THX AAA 788+ amplifier stage is the part that matters most to headphone owners: FiiO rates it for up to 780mW of undistorted (1% THD) output into 300Ω and up to 2000mW into 32Ω. In plain terms, that's a lot of clean headroom — the kind of output that makes hard-to-drive planar and high-impedance dynamic headphones behave like they're finally getting what they ask for.
Around that core, the K9 is unusually flexible for a desktop amp. The digital and analog sections receive power separately, which FiiO says reduces interference between the two audio circuits — a design choice aimed at a lower noise floor, and the listed figures back that up: SNR of ≥124dB (A-weighted) and a noise floor under 4.8μV on the single-ended output and under 9.3μV on the balanced output. Output impedance comes in under 1Ω into a 32Ω load, which is the sort of low figure that keeps the amp from coloring the sound of whatever you plug in. You get 6.35mm, 4.4mm, XLR-4, RCA and XLR outputs, plus USB, optical, coaxial, RCA and 4.4mm inputs — enough to sit at the center of a desk with a computer, a CD transport and powered monitors all connected at once.
The Bluetooth side is the quiet bonus. The QCC5124 chip with Bluetooth 5.1 supports LDAC, aptX Adaptive, aptX HD, aptX, aptX LL, AAC and SBC, so you can stream from a phone or tablet without a cable and still get a high-res codec. There's also a PEQ section in the FiiO Control app with seven preset tuning styles you can switch between, plus volume control and app-based control. The bundled accessories — a stand, feet pads, USB cable, power cord, headphone plug adapter and a fuse — suggest FiiO expects this to live permanently on a desk, and that's exactly who should buy it: someone with wired headphones, a fixed listening spot, and a growing pile of sources. Skip it if you mostly listen on the move. There's no battery, no carrying case, and at 2660 g it isn't going anywhere.
The FoKus Rex5 is the opposite philosophy: everything about it is built to leave the house. It's a true wireless in-ear design with Bluetooth 5.4, an aluminum enclosure in green, and an ergonomic earpiece shape that Noble describes as sleek and lightweight for a comfortable, secure fit over long sessions. In the box you get the earbuds, a charging case, a charging cable, ten ear tips, a storage bag and an instruction manual — a kit clearly assembled for daily carry rather than a permanent shelf spot.
The feature that stands out most is sound personalization. Rather than a fixed tuning, the Rex5 lets you tailor the audio to your own hearing profile, which is genuinely useful for earbuds, because in-ear fit varies so much from person to person and a sealed fit changes what you actually hear. The controls are touch-based, and noise control is handled through sound isolation — the passive kind that comes from a good in-ear seal, not active noise cancellation. There's also a built-in microphone for calls, so you can move between music and voice without pulling out your phone.
Battery is where the charging case earns its keep: the case holds a 500 mAh battery and charges in about two hours, and Noble markets long playback as a headline feature. The 0.3 kg listed weight is the packaged product, so don't read it as what's in your ears. The trade-offs are equally clear. There's no headphone jack, so nothing wired. There's no amplifier stage rated for full-size headphones. And unlike the K9, there's no LDAC or aptX listed in the spec sheet — this is a Bluetooth-first product aimed at convenience, not at feeding a home hi-fi chain.
Buy the Rex5 if your listening happens in transit, at the gym, or between meetings, and you want earbuds that adapt to your ears. Skip it if your main rig is a pair of 300Ω headphones and a desktop DAC — the Rex5 simply isn't built for that job.
• Best for driving demanding wired headphones → FiiO K9. Its THX AAA 788+ stage is rated to 2000mW at 32Ω and 780mW at 300Ω.
• Best for portable, cable-free listening → Noble Audio FoKus Rex5. True wireless with Bluetooth 5.4 and a charging case.
• Best for a desk-based multi-source setup → FiiO K9. USB, optical, coaxial, RCA and 4.4mm inputs plus 6.35mm, 4.4mm, XLR-4, RCA and XLR outputs.
• Best for calls and voice → Noble Audio FoKus Rex5. A built-in microphone handles hands-free communication; the K9 has no mic.
• Best for tuning the sound to your own ears → Noble Audio FoKus Rex5. Sound personalization is its signature feature.
• Best for hi-res Bluetooth codecs → FiiO K9. LDAC, aptX Adaptive, aptX HD, aptX, aptX LL, AAC and SBC are all supported.
• Best for a low noise floor on a fixed system → FiiO K9. SNR ≥124dB with a sub-4.8μV single-ended noise floor.
• Best for commuting and workouts → Noble Audio FoKus Rex5. Lightweight in-ear fit, sound isolation and a storage bag in the box.
In my opinion, these aren't rivals so much as two halves of a hobby. If I had to pick one, I'd buy the FiiO K9 — because it's the component that unlocks better sound from headphones you already own, it works as a DAC, an amp and a Bluetooth receiver, and its measured specs (dual ES9068AS DACs, ≥124dB SNR, sub-1Ω output impedance) tell a coherent story about clean, flexible desktop performance. I'd only steer you to the Noble Audio FoKus Rex5 if portability is non-negotiable — that's when its wireless freedom, sound personalization and charging case make far more sense than any desktop box ever could. Check the current price on Amazon before deciding, since both sit in very different budget brackets.
The FiiO K9, clearly. It has 6.35mm, 4.4mm, XLR-4 and RCA outputs plus a dedicated amplifier rated for high output into 32Ω and 300Ω loads. The FoKus Rex5 has no headphone jack at all.
No. It's a true wireless in-ear product with a built-in microphone and sound personalization, but no line outputs and no amplifier stage for full-size headphones. It's designed for listening on the move, not for anchoring a home system.
The FoKus Rex5 is the only one of the two with a battery — a 500 mAh charging case that recharges in about two hours. The FiiO K9 is a mains-powered desktop unit with no built-in battery, so it stays plugged in.
Yes. Its QCC5124 chip with Bluetooth 5.1 supports LDAC, aptX Adaptive, aptX HD, aptX, aptX LL, AAC and SBC. The FoKus Rex5 uses Bluetooth 5.4 but doesn't list those high-res codecs in its specifications.
They serve different needs, so value depends on your setup. For a desk-based wired system, the K9's dual DACs, THX amplifier and wide input/output selection do a lot of work. For portable listening, the Rex5's wireless design, personalized sound and charging case are what you're paying for. Check the current price on Amazon for both before you commit.
As an Amazon Associate I earn from qualifying purchases.
We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon and affiliated sites.
When you buy through links on this page, we may earn a commission from qualifying purchases at no extra cost to you.
Amazon and the Amazon logo are trademarks of Amazon or its affiliates. This site is an independent third-party review and is not affiliated with, endorsed by, or sponsored by Amazon or the product brands mentioned.