I recently had an M-Audio NRV10 and I had nothing but trouble with the inputs.
Adjusting the gain pot (on both XLR and TRS inputs), I could barely get any output until the knob was turned about 95% clockwise. At that point, the output would "pop" in and it would be clipping like crazy.
I talked to an M-Audio support tech on their forums and he thought it was a hardware issue. I had that unit replaced with a brand new on and I'm having the exact same problem.
Either M-Audio had a bad run at the factory with these or this unit just plain sucks.
I am still looking for a nice FW interface + mixer unit but I would stay away from the NRV10.