Depends which version. If they are the 80ohms I'd say the PA2V2 would probably work alright. If it's the 250 ohm version the Art may be beneficial.
Depends on the headphones. This offers quite a bit of power for the cost, but certain headphones will experience frequency response error with it. The PA2v2 is mostly a portable amp, so I wouldn't use it with severely inefficient headphones that also present a tougher load.
Alright good info, so on a DT 770 Pro?