what is a better power amp ?

Stick with the Pioneer for home theater. Your amps AND speakers should all match as close as possible for the best results. If you want to improve 2-channel then give us a budget and I am sure you will get more than a few budget amp suggestions.

If your receiver has pre-outs then you could upgrade with a seperate multi-channel amp down the road.

The polks are nice, a bit bass heavy, but nice...
However, they aren't easy to drive. Your receiver will push them fine in stereo. However, be careful trying to drive 5 or 7 of these from your receiver. The load may be more than it will handle at any mid to high volumes.

If you are thinking HT is your preference, you should have the same amp and speakers for the front 3 at least. Therefor, upgrading the amp will require a 3 channel (5 channel amps won't cost much more). Also, you won't notice much of a volume difference until you get into at least 200 watts/channel. You will notice a quality difference with most amp upgrades to a seperate amp.

I agree with the other 2 posts: Save your money and wait.

I agree with Viridian...listen first. Your speakers are rated for amps in the 50-500 watt range so an amp upgrade is not out of the question...I would however, listen first...save some money ($700-$1,500)...buy a good used amp at Audiogon down the road should you feel the need.

The Onkyo and Audiosource amps you mention are probably no better than the Pioneer in any large enough way (if at all) to warrent the extra expence.

Dave