I've had my 4311 driving my HT system for about a year now, with SS8s, center, and surrounds. For the vast majority of listening, it did absolutely fine. The 4311 is one of the best HT receiver values out there.
The difference for power comes into play with more dynamic or higher volume situations. In those cases, I almost always hooked in my older Hafler 500w amp to the LR mains- and it does make a clear difference. The Salks are now in their more permanent location not connected to the Denon but my recent additiona of an AVA 600r gave a big boost in clarity and speed any of the other power iterations(seriously- and I am generally a skeptic on theses things) for the sound. The placebo effect was tested via my musician wife, with a complete non-disclosure of what, if anything I had changed. She was able to point out differences that I hadn't even noticed.
Off-loading some of the 4311's amplifying tasks to a dedicated amp frees up some power for your other channels as well. If you can pick up a reasonable amp that you like, I think you'll be pleased.