In reply to:
The Yamaha running all five channels is only putting out 40-50 watts I read somewhere.
It is very important to qualify this statement as it is highly misleading. It is only
true when all five channels are being sent the same level of signal. The chance of this happening in a real-world situation is slim to none. What kind of listeners are your parents? If they like their music really loud and watch lots of explosive action movies, then this may be a factor. Otherwise, I wouldn't let that statistic sway your decision against it.
Also, would your parents be able to tell their system wasn't calibrated? I know mine wouldn't. You could let them use whatever device you go with uncalibrated, then calibrate it yourself the next time you dropped by.
As to the "sweeter sound" thing, I think I went temporarily blind and missed it. No comment.