Sound upgrade with new receiver?

[acritzer]

I recently upgraded all my speaker except the sub. Huge difference from the packaged Onkyo 520 stuff I had before. I still have the same receiver running though. So I'm wondering would I notice the same kind of improvement if I upgraded to a mid-level receiver?

Also how do "good" subs compare to others? Not to sound dumb, but aren't deep thuds all about the same?

Just trying to prioritize my wish list. Receiver, sub, harmony one, etc. Pretty set on my plasma and 5 speakers for now. Many years down the road I'd still like a projector, but that'll be a while.