1) If you start BetterSound after iTunes starts you need to stop BetterSound and select a new song before music will play.
2) All UI-based volume changes, whether on the OS-level or through iTunes are ignored.
3) iTunes track-seeking still doesn't work.
Right now you're kind of straddling this line between passive enhancement of iTunes audio and a dedicated playback program. I really think you need to choose one or the other because the middle is causing a number of problems with usability.
Personally, I think the issue with the volume isn't acceptable. Ideally, I'd like to be able to turn it off outright. There are already ways in OS X itself to change the volume by more than 20 steps even if you don't count simply dragging the volume controller. What's happening now breaks all but one of the ways in which you change volume in OS X and that way is buggy.
I'd rather see BetterSound go the direction of an entirely passive system that merely enhances system audio. All the complaints I've ever heard about iTunes have been it doesn't support some format and the sound quality is horrible. There are plugins for dealing with the various formats issue but nothing that really deals with the audio quality issue as I've seen. Rather than fighting iTunes I'd rather see BetterSound augment it to make it better, but that's just me.