Well, there are only one set of xlr's on the ua-5, so you would need to go sbd->rca->ua5 or sbd->xlr->rca->ua5 unless you think you can run mics->rca...hehe! You then would set the levels on the mics where you want them, and seperately set the levels on the sbd to where you want/wish they could be. Then, start phantom power on the mics and assuming signal from the sbd is fine, you should be good to go!
Daryan