I'm happy you posted this question! I have the same experience with my Peachtree 220SE. Based on the advice above I think I will try swapping the preamp tube.
MacIntosh c12000 preamp - Can not tell a difference between tube and solid state sound
I bought a used MacIntosh C12000 preamp. It is in pristine condition. Looks new without a mark on it. It is working great also.
Currently I have a Yamaha AS 32000 amp connected to it through main connects. It's just a tie me over amp until I find a good deal on a Moon amp. It is paired with Focal Sopra N1s.
One thing that urks me, though... when I toggle between solid state mode and tube mode on main , I cannot tell a difference at all. Why is that?