looks like youre wanting the digital signal mostly? how many channels does your Behringer have? provide phantom? if you have enough channels I'd just run the various mics into the Behringer then out into the recorder, or i guess you could get the appropriate cables and run it through the AD20 first to convert it, mixing it on the fly.
ps. what kind of mics are you using and what are you using to power them? the AD20 wont power the mics, its just a simple preamp.
I have a Behringer 802, never used it for recording at all, just for post mixing.