How much would I benefit from an amp upgrade?

Here is a diagram of my system. I tried the 140W ice amps of the pioneer SC37 but felt a huge improvement when I put the Denon POA amp in for the front KEF Reference 203's. (in fairness to the SC37, I didn't try biamping, which I still might experiment with on its ice amps) Now I'm wondering how much I would benefit from a higher end 2 channel or even 5 channel amp... Or would I be better off investing into something else such as a phono stage, more speakers or more music.

Usage:
33% analog music - 2 channel
33% Digital music - mostly 2 channel, some 5.1
33% Home Theater - all 5.1 soon to be 7.1

Budget: Varies but a multi-thousand dollar amp would be tough right now.
Ultimately if a big krell or threshold or classe or mcintosh would be a massive improvement I would consider it.

http://db.tt/IvNPKBvC

Educated opinions greatly appreciated.