Thanks for all the feedback, I'm looking into how to make it as simple as possible to install, I think it can be done without any need for soldering, and right now I'm waiting on a few parts to arrive so that I can try a few things out.
Basically the points for the 8 outputs are on the board already, there is no possibility of anything other than 4 stereo outputs, one each L+R for each of the voices, there is no chance that they will be addressable from the OS. Poly mode settings will dictate how the sounds are routed, which in itself could lead to interesting results. Having a voice output from the individual out will not remove it from the stereo mix, so for modular users this could be fun - you could for example have your regular mix coming from the main stereo outputs, then have individual outs being processed by the modular, like ANDing, ring mod, crushing, wave shaping filtering or what have you, then if you wanted to take it further you could mix these processed outputs back down to a stereo mix externally, attenuate them a bit and remove any DC, then send them back into the A4 inputs or into something else.
I am quite excited by the additional creative possibilities it will offer.
Rest assured, the quality of the kit will be the best compromise between cost and simplicity to install, whilst using decent parts throughout. Anyone who has bought one of my other mod kits will know that I provide clear and easy to follow instructions etc.
Probably not going to happen until after Xmas as many other things in front of it