It's probably just me, but I think the DT531 + creek obh11 combo sounds better than the 770pro with any of my amps

There's a couple of things that bug me about the 770pro - it's recessed midrange for vocals (john hyatt sounds like he's standing behind the band), the closed-factor (uncomfortable in hot weather), and they're not quite as comfy as the 531s.
I'm not bashing the 770pro at all, it's a great headphone - but I really do prefer the 531 when amplified and that goes for any combination (770pro/Mghead vs 531/mghead vs 770pro/creek vs 531/creek).
I'd avoid the 831 and 931, they're both great sounding headphones but I never find myself "rocking out" with them at all, the detail becomes far too distracting
especially with not-so-well produced music or more harsh sounding stuff (autechre etc).
As far as the 990pro goes, I find the bass to be slower and less responsive than the 770pro.. which isn't a good thing when you've got as much bass as these headphones
