Smajdalf:
I still think the many MCU solution is good.
It's a fair suggestion, they would basically act as 22 bit I/O expanders while not quite being such a matrix scanning hell.
However, I'm currently looking at setups like parallel out shift register switch multiplexer | Open Music Labs
and wonder if this wouldn't provide a much better solution?
In total I have 410 I/Os to and from the µc and that's not counting in displays and SD cards any any other interfaces, so whether I use I/O expanders or a lot of Atmegas, it would still boil down to very very many ICs, which raises another question: I will probably have to design two boards, one control interface board and one mainboard, regarding SPI I'm reading that my traces can't go off-board or else data will be lost to capacitance, is this an issue with 2 boards connected via pin headers aswell?