Thanks for your help. I will check tonight but I'm 80% sure the problem exists with both inputs. One is high gain and one is low. Also there is a "bright" switch which does increase the highs somewhat, but doesn't eliminate the muddiness.
Start with the obvious things like making sure all of the supply and bypass caps are new. Once you are sure the amplifier is working as intended when new then you can go in and make changes as necessary to make it do what you want.