When I got my PC-Ultra, I was actually patient and calibrated everything before letting it rip. I was very, very impressed once I got it set up. It sounds like you've gone through that now, but if not...do that first. Get all of the channel levels set with the SPL meter.
I don't know if the Avia disc has it, but I recommend running through a sweep of frequencies and checking out the response (with the SPL meter) at your listening position. You can download a sweep, but I bought a disc from AV123 for $5 and it worked great. It really helped me to set up the tune of the sub (10Hz, 15Hz, or 20Hz), the PEQ, and the room size calibration switch. I was able to get a fairly flat response by adjusting those three items.
I agree with Warp. Unless you got a bad unit, you will be quite pleased once you get it dialed in!
Adam