I have a Pioneer vsx9130txh and cant wait to replace it. You should try yours first, of course, but mine sounds like it's strained when I bump the volume up even a little bit over modest levels. Thin like popeyes wife.

I am driving 4ish ohm towers set to full range and there is not enough grunt to get the wow I know the speakers are capable of....

I would drive your center and mains with an external amp like you are thinking.... my 0.02. wink