B&W 804 off of a Sony Receiver???

The only possible problem is if your receiver does not have enough power, and you play it very loud, 'clipping' may occur which would probably damage the speaker. If you like it loud, and hear distortion, turn down the volume.

you are more likely to damage your frame of reference...

Sony receiver from the 70's are cheap but doesn't sound bad atall. If your receiver is over 50 watts, you can actually use it with the 804'without any problem as long as you don't play it too loud. You could also damage your speakers or any speakers even if your using a 400watt Krell or a MBL amp. if you overload your speakers by turning the volune too high. Anything that clips is bad for both the amp and the speakers. These are just the basics. On the contrary, you should have bought the 805's or other speakers with higher efficiencies if you're going to use a low power amp. Just makes no sense.

Thanks for the advice guys, I'll keep it low for now. Just had them on at the fish store where we have an NAD 75W Receiver and they sound great.

I bought the 804s because I wanted a fuller sound from my speaker. I'll be upgrading to a nicer amp as one comes across at a decent price.

Audio_99,

Actually the 804's are more efficient (90dB spl, 2.83V, 1m) than the 805s (88dB spl, 2.83V, 1m). In fact, the 805s require a lot of power to provide maximum returns.