(1) DeviceexaU2I is USB to I2S (x4) device from exadevices.com, $430 + FedEx.
(you can refer this chapter for other sound device, of course. for example, HDMI PCM 8 channel out + AV amplifier can be simple solution for 3 way crossover system)
I'm using Reaper. Personal License is $60.
How to configure
Install foobar, then add foo_out_asio.dll here.
Install Reaper, and select "ReaRoute ASIO Driver" additional component.
Install exaU2I. (see install guide of exaU2I)
foobar configuration, how to map output to device.
Reaper's Option - Preference - Device is ASIO, exaU2I ASIO DB, 8 ch.
Now you will work on Reaper.
Reaper's track area, right click and "Insert virtual instrument on new track..."
Select VST: ReaFir
If you want 3 way, repeat again and again
press track's "Input: " selection. assign ReaRoute 1 + ReaRoute 2, for all tracks. (LOW, MID, HIGH has same input)
press track's "I/O". disable Master/Parent send. for all tracks.
"Add new hardware Output..." then select "Out 1 / Out 2" for LOW track.
Now track 1 get input from ReaRoute 1/2, output to ASIO Hardware 1/2.
Track 2 = Mid, input from ReaRoute 1/2, output to ASIO Hardware 3/4.
Track 3 = High, input from ReaRoute 1/2, output to ASIO Hardware 5/6.
press track's "FX". modify frequency curve, for LOW, MID, HIGH. This is HIGH example
If you want you can add more VST like spectrum monitor, delay, EQ etc. this is topic inside Reaper and VST.
This is LOW example
This is MID example
Running now. shows MID input and Result.
Do not press this button. This is "FX Bypass" button. When you press this button for "HIGH" track, The High Pass Filter will be bypassed, then full music power will go to your tweeter.
Now you have 3 way crossover, full digital RAW I2S signal output from PC. enjoy.
This is FFT channel divider. I also have pure FIR channel divider.
You need nVidia CUDA enabled graphic board.
SSE: you just need powerful CPU.
AVX: you need SandyBridge AVX enabled CPU, and Windows7 SP1.