I am not sure for HT, bur from my experience with stereo, I noticed a great improvement going from a receiver to separates. I had before a Rotel stereo receiver. It is not only a matter of more power (watts) but also separation of function, leaving the power duties handled by a power amp, and processing duties handled by a preamp.

Axiom M60s, QS4s, VP100 Onkyo TX-SR804 Oppo 970HD Rotel RB-1080/RCD-1072 REL Q150E sub, PS 3