Well I only listen to 2ch audio and my system pulls double duty as HT as well. I sold my center channel and use my receiver to power my surround speakers. For my HT needs, I NEED to have a subwoofer and surround speakers. I decided I can live without the center channel although I do miss it.
So you can spend the money on a 5 ch amp and maximize your budget to improve your HT performance or you can get a 3ch amp and put more money into your 2ch system without sacrificing too much of your ht, or you can get a 2ch amp and maximize your budget for 2ch performance and sacrifice a bit of your ht performance. Unless you plan to go separates for your HT, you might not notice too much of an improvement by having separate amps powering your surround speakers vs your receiver.