I have owned a Denon AVR, and I agree with the comments that you can expect a significant improvement from better amplification. Several posters have suggested Pass Labs, and I think that is a good choice. I have owned two Pass amps, and they fit your description of "neutral, but a shade on the warm side." I have not heard your speakers, but I read JA's review in Stereophile, where he mentioned that...
[The Synchrony One's] superb retrieval of recorded detail was accompanied by a slight lift in the presence region. This was not nearly so much as to add brightness to the balance, but voices were presented as being more forward in the mix.
I mention this because, in my experience, Pass amps could be described the opposite way. Combining the two might therefore result in a nice balance, given the preferences you described. Good luck.