+n to what our other friends said.
If you want your "system to sound better", before spending money on an amp, I would:
-Get a new sub
-Experiment with speaker placement
-Experiment with wall coverings or sound treatment
I don't know how loud you are listening, how big your room is, or what content you're consuming. It's unlikely that the amplifier section of your receiver is the weak link in your system, or that buying a new amp is going to make the biggest difference for the money.
I bought a 3-channel amp for the L/C/R channels because it made me happy. I'm pretty sure it did NOT make an audible difference for the overwhelming majority of things I watch/listen to. But I'm still glad I did it.
