is the board feed analog or digital? im assuming analog
run your mics int he front like normal, and you can adjust thier gain like normal. run the board feed into the rca inputs in the back, and you can adjust the signal on the back with that little knob
i dont think you can actually give gain to the rca inputs, i believe that all the way cranked up would just be line level... maybe i am totally wrong on this certain point, its been awhile since i had my ua5