Multiple Amp setup is my guess... Everytime I play through 2 or more amps at once at quite high volume it's a pretty thick sound. At rehearsal I always played through my OTS and an old Echolette Leslie; now a Fender Twin and the Leslie (don't have to carry the twin ). The sound is huge. Maybe the different frequencies compliment each other or something like that, I don't know.

Another thing: Ika suggested the 470pf setting for JM sound. And this setting is also pretty thick. Not as fat as with the missing NFB though.

Edit: Okay, I just noticed I didn't answer the question at all xD Okay, next try: Maybe it's just the style... If he'd just play powerchords with that thick sound it could be problematic? I also don't see the guitar as a part of the whole mix with the most older songs (WTLI), it's more above all other instruments like a lead singer. Hope you get what I'm meaning...

I saw Mark Knopfler live in 2010 and his sound was even huger. But again it was more like a lead singer and not a part of the background music. I think it also has alot to do with volume...

Yes I think you're right. Next time I have an opportunity I'll try and see the headroom of the input vol. In mid december I'm playing a big hall. I hope I can bring this and a 1x12. Basically it like carrying the rig into a mall.