I agree with Jason. It seems to me that you are over-taxing the Onkyo. That, coupled with most likely not only a "crappy" sub, but one that isn't in the optimum place in your room, and you are getting all sorts of horrible sound. The surrounds, while they may be cheap, aren't going to be the *biggest* source of poor sound for you as the sub and amp are throwing more noise into the room from the mains and the sub, unless of course your surrounds are turned up too much and then they are going to be adding to the terrible sound.
There are lots of suggestions you can be given, but some will require more money, or at least a bit of work to get things tuned to your room better. I have M60 fronts with the VP150 center (and QS8 surrounds) and I can actually hit positive numbers on my receiver (Pioneer Elite) and it sounds nice... VERY loud, but not distorted. Note: I've only done this a couple of times as a test of the quality of the Axioms when I first got them. I usually watch movies around -15 to -18 when it is just me watching, and about -18 to -22 when it is with my wife as she doesn't like it "so loud." Sounds great in my room, and I know if I could get off my butt and tame the room a bit with bass traps, etc, it would be AMAZING!
Hang in there. We'll help you out. Just keep in mind that you DID buy better speakers than a HTIB system, and while I would say that this is far from DIY, I understand your frustration and again, we'll help you out.
What sub and surround speakers do you have?
