K so now I'm deciding between Energy RC-30 vs. B&W 300 or 600 series (which ones??), and Yamaha RX-V661 vs. Rotel or Denon receiver. What do you guys think?
The Yamaha 661 is a fine receiver, especially for its price. I might get one. Rotel makes good equipment, but it's more than your parents need. Denon makes a large range of audio-visual receivers (AVRs). Many people love them, and they're usually well reviewed. One knock against them is that their set-up menus aren't the easiest to follow. Maybe that's changed in the last year.
You might look at a Yamaha RX-V659, which the 661 replaced. It has everything your parents need, and will cost about $100 less than the 661. You can read a detailed review of it on the main Audioholics site.
I'll thrown another set of speakers your way. Look at this pair; it'd be all your parents need if they can live with fine 2-channel sound:
AV123 Strata Mini
http://www.av123.com/products_category_brand.php?section=speakers&brand=54
People here have recommended many good speakers. But, since an ordinary piano's lowest note has a frequency of ~27.5 Hz--some special concert grand pianos have extra bottom strings and go even lower, but these are rare--I recommend either getting speakers that will go to about 27 Hz, or get a subwoofer to augment speakers that don't.
The Strata Minis I recommended play frequencies from 27 Hz to 35,000 Hz, plus or minus 3 dB, which is acceptable on the low end. The Minis have a built-in, self-powered subwoofer in each tower to handle the lowest notes.
If your parents enjoy a lot of pipe organ music, then you might want a separate subwoofer that'll produce good sound levels to 20 Hz, or even lower (these lower notes can't be heard, but they can be felt). A fair number of pipe organs have a 16 Hz pipe, and at least two in the world have an 8 Hz pipe.
(What's the purpose of those if the average lower end of human hearing is 20 Hz? The extra-low notes produce pressure that can be felt though the air and can be felt through the floor. Plus, if you're in a hall when a 16 Hz note is played, you'll feel it and you'll hear it's next overtone. But notes this low are rare. I have a degree in classical music and I've written pipe organ music, yet I've never come close to writing a 16 Hz note in a score.)
Even if you opt for a surround system, I still recommend getting one that will play notes down to about 27 Hz, even if it means adding a subwoofer to make it a 5.1 system (the ".1" refers to the "low frequency effects channel" (the "LFE")--the sub. All the AVRs you mentioned will handle a 5.1 system well.
For a good explanation of the various sorts of amps, pre-pros, and receivers, see post #9 in this thread:
http://forums.audioholics.com/forums/showthread.php?p=272630
Chris