When going to the 23dB setting, the thing that comes to mind immediately is that the soundstage compresses both side to side and front to back. Low end seems to tighten up and you lose some of the "air" compared to the 29dB setting as well. Still continuing to form impressions.
D.D.
D.D. Interestingly, when I use the 23dB setting I get just the opposite effect - better blacker soundstage. It is noticeably better in terms of depth. Overall, the sound seems more controlled and balanced. Of course, I can't explain why we each get a different result, but I wouldn't be surprised if it has something to do with other differences in our respective systems.
Dave