AD8610 has very nice soundstage in SM, if it's not the case that I have unique ears
I had my SM with AD8610 for four months and its soundstage really impressed me. From last month, I got my SM reconfigured to be a socketed issue and rolled in some OPAMPs like (AD8610, AD825, OPA227/604/627/637, NE5534 and LM6171).
When using HD600, AD8610 did has the widest soundstage, though not the deepest, but still deep enough to articulate the layers of music. It's more forward and brighter than other OPAMPs I tried. I think that's why I feel a closer soundstage with AD8610. LM6171 has the deepest soundstage but kind of narrow. OPA627 has a 3D soundstage in a pretty good shape, but neither the deepest nor the widest. AD825 has a very similar sound sigature as AD8610 but not as relaxing. So far, AD8610s are still my favorite to cope with HD600 that's kind of dark.
Probably Xin implemented some different designs for SMs that make AD8610s sound diferent. But it's worthwhile to give AD8610 another trial.