Yep solid state Rolland will hit the spot. The JC120 is an absolute classic for clean sound. I think PonyOne had one for a while. Also a tube screamer can work really well to take some of the shine off as required !

ANother thought, how about feeding a cheap Preamp like an ART TPS into the FX loop return of the Marshall ? You could use an ABY box to flip between the main in going into the amp for the dirty channel and a second input feeding the pre.