Amplifier: Needed? If so, any suggestions?

[GBMidge7]

Hey all. I posted a question awhile back about an amplifier and never got a response so I figured I'd try again. I just got my sweet tax return back, and I am planning on spending a portion of it to upgrade my front speakers. I will be purchasing 2 Polk RTiA9 floor standing speakers, and I feel like my general AV receiver (Yamaha RX-v663) won't be powerful enough to do them justice. As such, I am thinking I should also get an amplifier, but I have NO idea where to start looking for one. I was thinking a 3 channel, to power the new fronts and my center. I am pretty sure my receiver is capable of an external amp, but can you all confirm this as well for me? Any B & M store I have gone to has been crap in terms of having anything, so I figure online is the way to go. Can anyone suggest a decent amplifier that will give me a bit more power for not too much money? If I HAD to put a price limit, I would say less than $500 easily, and hopefully less if possible. Thanks in advance for the help, I hope I get can get some answers this time!