Personally I like the AD826 at the moment with the 7520, but I'm using Grado 325is with G cush pads which aren't very dark sounding anyway and bring over a lot of detail. LM4562HA, AD826, and OPA2107 are my favourites. The OPA2107 smears detail a little too much even though it sounds nice. LM4562HA can be a bit bright in the highs at times but can sound very deep and wide with good bass. AD826 is the king of detail but the bass can sound a little lacking in warmth at times, and can show up some harshness on recordings, but it's very clear.

I'm still using the 12V PSU though so I want to upgrade. I'll probably plump for the maplin one but I'm not sure which connector I need into the DAC or whether I really want a bench supply like I'm in a lab.