I'm not seeing a lot of praise for the OPA2134, but am seeing some good things about the OPA627/637. As for the AD8620, reviews seems to be the same as they were before: rather clean sound, and can be too steril with the wrong associated circuit. I may just solder in a few sockets and roll these until the rest of the changes are made.
Additionally, it doesn't look like these are biased to Class A, but I'll have to poke around at the traces to figure that out. I'm doubting it, though.
Opamp preferences, anyone?