The problem is, to put a more fine a point on it - your speakers suck. If you go too loud with them, THEY WILL DISTORT, no matter what you do, or how many receivers you hook up. If you maybe JUST go with the Pioneers, you might be OK, as you said t hose sound better and "louder". As soon as you put those other speakers from the HTiB into the equation, your sound is going downhill, no matter how you do it, and it won't be worth the tiny bit of loudness increase you get. You're asking to do something that will NEVER sound good.
The ONLY way to make it sound reasonable at a loud volume is to get better speakers. Otherwise, just give up, and take whichever set of speakers sounds better (or louder if that's all you care about) and use those. We're all sorry that this is not the answer you want - it sucks, it really does, when you can't just make things work, but that's life. There's a reason people spend so much on this stuff - it's not possible with cheapo equipment.
