i also have a xxx

smaller cabinets make it sound tighter..higher wattage speakers make it sound cleaner.

it sounds like your seeking the same thing i was,...i wanted note definition,..but not at the sacrifice of a very very heavy sound..(bass u can feel)

here's what i have done to get it.
-standard tuning..(was c#)
-lighter guage strings...9's
-dimarzio drop sonic in the bridge..(i went through 4 different pick ups)
-less gain...
-got rid of the marshall cabs (1960a/1960b)...got mesa recto cab and a traditional cab,...
-add some level of mids


i havent done it yet but all the guys on the peavey thread swear by the el34 tube change,..right now i am very happy with my sound...

good luck


jessexxx