Well, that behringer ada8000 or whatever the model name is, is an 8-channel preamp with built in converters and digital out.
So you could use that as analog ins, and then run the adat digital out into a card that accepts adat like one mentioned (btw, I'm very interested in taking a look at that, thanks a lot for the info).
So basically, the ADA is your mic input, and then it all goes from there digital to the card, which gets it into the computer...
You wouldn't really need your other mixer for anything, cuz you'd have 8 inputs, and each would get to the computer as a separate channel.
You could still get some use out of it for other things though, like mixing down multiple things to one input, if you need more than 8, or maybe setting up headphone/monitor mixes.
Kinda nifty stuff...
There's also more expensive pres with a/d converters, like
the M-Audio Octane (the chassis looks cool! hehe), and then there's also more expensive cards with adat in, such as those by RME which have a pretty good reputation, but are also more expensive.