But what I am saying is, you are not going to notice a difference until you push the avr beyond its limits {or close to} sure the more headroom the better, but its not going to make the sound "great" at lower levels, an amplifier is an amplifier... An $18 lepai 2020i will sound just as good as your grande until you push it close to or beyond its capabilities... Since you are running efficient speakers, you don't need much power to make a lot of sound, so you are not going to see any benefits in sq with more power....
Get a better set of speakers and you will get better sound...
like acu said, same level same sound {unless you are trying to get a higher level out of the avr, for instance you want 98db at 25 feet and only have 80w when the speakers need 80-100 to do it, you will run into clipping and all kinds of issues.. As a rule I don't like to push an amp past 70% of its capabilities, that leaves 30% headroom, if its for HT, that is more of a burst of poer here and there with the hard ranges taken care of by the subwoofer, music is a different story...