If I understand correctly, you want to process the audio on the computer using Max/Msp or a DAW and use Bela only for audio input/output? If this is the plan, then maybe you would be better off using a soundcard for your computer, as long as you can live with the minimum latency constrains it comes with.
Bela is not quite a soundcard, you can think of it as sort of a soundcard+computer in a single package, if you will, which is what gives it the low-latency performance. As such, the audio processing should happen on the board and a restricted number of audio programming languages can run on it, at the moment these are C, C++, Faust, Supercollider, PureData, pyo. The limited number of supported languages is due to the fact that part of their code has to be rewritten for it to integrate well with Bela's software and hardware environment.
As you say you are familiar with Max/Msp, you may want to have a look PureData, which follows a similar paradigm, being created by the same original author Miller Smith Puckette ( msp !).
PureData, in its Vanilla version, is almost entirely supported on Bela (with the exception of the objects listed here ) and could probably be a good environment for your project.
While there are ways of sending audio to/from the computer (over network), this comes at a the expense of a few hundreds milliseconds of latency, which I am sure is not what you want for your application. There are - however - ways of using the computer as a GUI to control the real-time audio task running on the board, if this may be of interest to you.
Regarding preamps, you could use the onboard Bela preamps and just use something like this to give phantom power to your condenser microphones, or use microphones which can be powered on battery (e.g.: AKG C1000 ), or use a full two-channel pre-amp unit like this (note you would not be using the USB connection on the last one ).
