The PA-504 is so versatile that you can configure it in quite a few ways. If this were my system, I would add a subwoofer. Then wire it like I wrote above, except you power the rear coaxials with the radio instead of the amp. Ideally, you want just some rear fill so the front sound stage is not lost. Thus, less power to the coaxials would be good. Then you bridge channels 3 & 4 on the amp to power the sub, and activate the low pass filter. That would give you 50w per channel up front, about 25w per channel in the rear, and 175w mono for the sub. End result: a nicely balanced 325w total
