Grado PH-1 Modification

My PH-1 stopped working after I disconnected the DC power connector before unplugging the Wall Wart. It now hisses and crackles on both channels without passing a signal. Grado can fix it for $75 but I'm leaning more towards doing it myself and using better components while I'm at it. First off, the DC power is a little unbalanced (+12.4 -11.6), which may be part of the problem. I doubt it's the op amp as it is amplifying, I feel it's one of the capacitors or resistors. But then again, it could be the op amp since the problem is in both channels. I just haven't tested and traced yet.
Has anyone upgraded their PH-1 and improved the sound using better capacitors? Is there another op amp you would recommend that's better than the stock? Any suggestions would be appreciated.
The schematic is available online for reference.