I just picked up a used AD50VT-XL 2x12, in very nice shape. Almost every channel is a high gain channel, even the one clean channel it has will break up unless you totally dial back the gain and control your volume from the guitar. Effects are much fewer than on the VT+ series amps, but to my ear they sound more refined. The dirty channels on this amp are truly awesome, this is a metal player's amp right down to the blacked out diamond metal grille.
Now my only real gripe with the VT40+ was with the snare brush sound on the high gain channels. So I put the channels on the AD50VT-XL through a good listen - there's no noise reduction to be found on this amp, by the way. Turns out it doesn't need noise reduction - it's pretty quiet. The snare brush effect is still there, interestingly enough, but it's very quiet to the point where it's almost imperceptible. I have to really listen for it, and it's so light it's almost more like a bit of hiss or just noise than a "snare brush" type of sound. Big improvement there - bummer it's on a valvetronix model that is two revisions old...!
This amp is fantastic, it delivers a nice palette of high-gain channels, all of which sound very good, even if a few are probably very similar. The effects it has are all I would want, and they do not add a lot of noise and sound very nice and rich. Interestingly, one of the channels on this got a bit noisy when I placed my right hand near the strings/pickups. Very strange, as if my hand were emitting RF or something. Once I moved it away, dead quiet. Only one channel did this - odd.
The VT40+ will be getting sold since I cannot return it anymore. My guess after now comparing old and new is that they might have used better AD/DA chips and maybe some better electronics. The build quality on this is noticeably better also, with corner protectors, etc. This isn't noise-free, but definitely much quieter and to my ear sounds better than the VT40+. That this is a "high gain" amp and doesn't even have a noise reduction on it kind of says something, though.....