Frog offers some excellent suggestions. Interconnects, isolation shelving, cones, pods, tube rolling, even speaker cables will all influence your results. Also try experimenting with different upgrade AC cords, not only on the preamp but also the source components & power amps. If you haven't tried AC cords yet then begin at the preamp, then the PA, then the source (you do the source last because if you do that first then all later downline tweaks will influence the source too). There is a whole lot that can be done to tweak your rig; certainly it's salvagable & if you're dedicated then it can be simply delightful.
