Just tried OPA627AP and AD979ANZ for a full day each. The OPA627 goes very deep in the bass and adds more attack and impact. Overall sounded fuller than ADA4627-1A but at the expense of a slightly recessed mids and highs. It also feels the soundstage is narrower and instrument separation sounded closer than before.
On the other hand the AD797 has on par bass impact and attack but not as deep and full as the OPA627. It has the soundstage, separation and clear details of ADA4627-1A but without the sharp edges.
What surprises me is the tone and timber AD797ANZ brings is very pleasant, mids and vocals have very unique texture and overall the sound is more closer to the natural presentation of a live performance with a very quiet background. I am not expecting this result because I read a lot of comments about this opamp which is very picky and unstable on some circuit at unity gain and all the bad raps. I never considered this opamp when I was making a choice of opamps when buying the 6SMKII. But on 6SMKII it really shines imo. Maybe it just strike the right synergy with my gear, DX50 + RB and the Roxanne @ 0dB bass.
I thought ADA4627-1A has the right balance with clear details and wide soundstage. But for my ears, AD797 is better. The OPA627 is the odd one here, it has the bigger bass, fun to listen with but sacrificing soundtage width and mid/high details. ADA4627 and AD797 is more or less similar. Where the ADA4627 reveals the raw details of the music, the ADA797 presents it in a very pleasing smoothness and texture.
