Okay, so the receiver is a keeper!
Now, let's talk about that subwoofer. You can do better, and I mean better as in a cleaner sound, not necessarily room rattling bass. If you're looking for a true sound quality upgrade a sub (or 2!) Is a viable path for you and I think you'd be surprised.
I had a pair of subs of roughly the same size and quality of yours (
Klipsch RPW10s) and when I upgraded to something from a company who actually specialize in subs I was shocked at how much better my whole system sounded. Like I said it wasn't about getting more bass, it was clean bass. In fact at first I mistook the lack of distortion for lack of volume because they "seemed" quieter! I'd never heard good, clean bass from a legit sub in my room before. It was, I'd daresay, a revelatory experience.
Most people don't know what they're missing until they hear it. It was like getting glasses for my ears. You could try something from SVS (or a few others I can't think of off the top of my head) who offer risk free trial periods and see for yourself. If you're dissatisfied for ANY reason they'll give you a full refund and even pay the return shipping so it truly is risk free.