My TT set-up is more budget than yours and I found a really nice improvement going to a Hagerman Bugle2 phono preamp. It is a little more expensive than the Cambridge Audio 640P but it also doesn't have a rumble filter that I'm kind of needing right now.
Another step up from the 640P that I've only read about but is a couple of hundred dollars more would be the Jasmine phono preamp 2 or the Jolida JD9 phono preamp.
Another step up from the 640P that I've only read about but is a couple of hundred dollars more would be the Jasmine phono preamp 2 or the Jolida JD9 phono preamp.