Moving up from Marantz 2325, to new amp and preamp

I have lived for years, happily, with my numerous, rebuilt, Marantz 2325's--mated with Castle Speakers, and Oracle Turntable-Cal Audio, CL15

Recently having conversation with audiophiles about improving the power side of equation---suggestion for slightly used Bryston Amp, pre amp--I have no experience with this equipment. I have found some of the modern equipment either "harsh" or lacking the "drive" of my 2325-

trying keep investment at $5000 or below (realistic?)--would welcome your input, re: your suggestions for what might be improvement in sound quality---want to keep sound "warm"---"English"?--Nothing with overly high highs or booming bass--all feedback is welcome--