I checked in with Alex this morning about the portable amp, and asked about the Carbon status. As of 11:50a Pacific Time (-08:00), there are only 39 Carbons remaining.
Lol, that's impossible, no one ever listens to me.
Definitely the ETHER (open-backed), no question. It's the most neutral and balanced of the three, which plays well with the Carbon's own balance and transparency, in being suitable for the most genres (I listen to every genre with the exception of four). On top of that, and this is something that many have experienced, there seems to be special synergy that exists between the Carbon and the ETHER in terms of better dynamics. It's rather thrilling, and unexpectedly so, for a pairing at their combined price range.