Actually from what you have posted regarding the mixer, you seem to be happening. But just to cover it:
a) No midi magic needed. Midi only mimics the physical controls.
b) The digital 'A' interface outputs are 'locked' to the outputs of the 8 internal busses (the digital 'B' port is user assignable). What ever you wish to record from the digital 'A' lightpipe must be assigned to the 8 internal busses.
The quick setup is to assign the first 8 channels, one to each of the 8 busses. ch1 to bus1, ch2 to bus2 etc. Make sure your bus out levels are up. You will now have the first 8 faders correspond to the 8 digital outs of the 'A' lightpipe. Provided you have assigned inputs to the channels and supplied signal, your lightpipe is 'hot'.
It sounds more like 'arming' multiple channels to record from the 1212. That I can't help you with.