I've had a go at this a couple of ways; two great big 17-way MUXes which connect to the array of pins works fine, but has the downside that you nothing prevents you connecting both DACs to the same analog pin.
Why would you not know which pin mux A is going to and mux B, that is simple code to
test for a collision when you are selecting the channel ? Unless the muxes were HW driven
and even then the HW could test for that.
Maybe I do not fully understand the problem.
Yes, it's certainly possible in software to prevent accidentally connecting both DACs to the same pin. I simply hoped there was a more elegant solution.