Grove (link) is a modular, standardized connector prototyping system. It is a convenient way to expand an Arduino or other microcontroller board.
The system consists of:
Conrad offers some microcontrollers with Grove connectors attached to the main board in their C-Control brand.
Audio connectors could be implemented as Grove components. Just soldering the wires to a stereo audio jack and providing a Grove connector on the other side.
This would plug into an expansion board or directly to the main input board (Arduino).
Once the prototype is complete, the input electronics could be created as a custom PCB in the form of Arduino Shield. The above connectors would then plug into this board. Something like this: