I disagree about the XXX being louder I have owned both as well ,and the 5150 definatelyt has more ball shaking capabilities. The XXX , while a good amp, doesn't come withing the vicinity of the 5150 in power. You stand in front of that fucker and chunk with the volume on 3 and you can feel it resonating through your body. The triple xx is cool and all and definately has a cool voicing in it's own right and it's definately got that peavey sound, just doesn't deliver that chest thumping powerfull grind.
Im not sure you read my post correctly though...
Its louder with the Effects Loop engaged.
Stand alone, the XXX has to have the volume knob turned to about 6 or 7 to match the 5150 on 4.
I put the send and return level knobs at 12'oclock on my triple xxx and it gets louder than a Krankenstein and keeps a nice tone in doing so.
Without the effects loop, you are right.
I dont know how many people have ever tryed a Bellari Sonic Exciter, but it sounds awesome.
12ax7 tube driven, not processed sounding like a BBE.
And at about $379 I figure not many people have actually tryed it.
That in the XXX Effects loop with the levels up at 12'oclock, smokes!
It sounds killer on the 5150, but the 5150 still turns to mud after 4.
I like to think of it as a Secret Weapon for crushing tone.