Monk, so far as size of speaker, your present room wouldn't require M80s as compared to M60s and I think that M60s would be fine. It isn't clear when you mean to get into multi-channel rather than stereo, but I assume that you want to get a multi-channel receiver now so that you're ready. There's no good reason to consider tube equipment and an excellent receiver in the price category you mention would be the Pioneer 45TX which you should also consider besides the Denon 3803.

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Enjoy the music, not the equipment.