Hi

Hmm, what about a stackable matrix mixer system

Basically a matrix mixer is the same as an audiomixer with aux busses
(except that the matrix mixer is DC-coupled, te audio mixer is
AC-coupled). So it is the easiest to adopt the concept of modular audio
mixers:

One summing module with the outputs and one input module that
distributes its signal to five busses. The bus system could be realized
with the well known 10-way ribbon cables.

The input modules could be switchable for DC or AC coupling.

Also an option to add such a module some day as AUX-send in a modular
audio mixer system could be worth a thought.

Florian