Need an amp for my B&W

[wackydesigner]

I have a B&W Nautilus 804 and just bought a Kimber Kable 8V. Right now its hooked up to a $150 Yamaha 5.1 receiver and the sound is just not even close to what I want. I need to buy an amp under $600. Now, I'm not buying a new one. Definitely used from Audiogon. I don't want a bright amp like Rotel 1080, although its got great reviews. Don't care how old it is as long as it was made after the 90s. Can anyone help? Now, for a more pronounced effect, should I replace the receiver? Or is most of the quality depended on the amp?

B&W recommends 50+ WPC, but I've also heard that for high end amps like McIntosh/Classe/Musical Fidelity, 30W per 8/ohms are ok.

PS: I need specific model #s. Thanks.