The backbone of the whole MYMU project/system is the backplane. I am using the Prarie-4, a four slot backplane, as a starting point. From there, it's easy to add more slots or to double up on the backplane cards for more inputs/outputs.
On the backplane, there is an input bus as well as an output bus. Input cards naturally will connect to the input bus. Each input will be selected by a controller of some type to put the signal on the bus. Input cards can be anything from a basic opamp based buffer to a USB soundcard for your computer.
To connect the input and output buses you would use some kind of control card. It could be a simple volume pot and selector switch or something as complex as a processor applying DSP functions to the audio signal.
On the output side of things, you have multiple options. You can do low level output with opamps, discrete components, or if you're so inclined...tubes! Power amplifier stages could be used as well. I will be making a simple 30WPC output stage so that I can use my completed crate as an integrated amplifier.
I will eventually do higher power discrete and tube output cards. The current card footprint will not fit so I am going to make 2x and 4x sized cards that will be backwards compatible with the original that I am working on now.
Other Future Plans
-DSP room correction card
-Oscilloscope card (for trouble shooting other audio projects)
-Rasberri Pi / Beagle Bone card for internet enabled audio control.
Very interesting, I've been looking around at different audio projects. Are you still working on this?