The Gr07 are off my list (for the moment at least) because I think that they would be too lean, and I don't need another monitor like sound with my B2, how is the isoletion and confort on the ATs? I hate the ambient noise of the city and I have little ears, so fit could be an issue.
The ckm500 is comfortable. Also, if you like your HJE900, I think you will like the ckm, they are closer in sound sig compared to the other options listed. I never had the hje900 and ckm together at the same time, but from memory I think their overall sound quality are not that far apart. The eterna on the other hand, is a completely different animal.
Yes I know that the Panasonic and the Eterna aren't similar in the sound signature, but they are very bassy and fun to listen, and since I don't have them anymore I want an upgrade but still being bassy and fun, my B2 doesn't lack in anything, but I remember that the Panasonic (and subsequently the Eterna) had more bass, more rumble if you like.