I got my AK240 last week. I have compared it against my AK120 and Calyx M. I am mainly using JH13 Pros, but have also tried the AT-M50x, Senn HD25s, HD600s and LCD-Xs (amped and unamped).
So far I am disappointed. It sounds very similar to the AK120, which did not impress me much either. While it is very detailed, it still sounds a little "small", with a lean, slightly constricted sound, and also a certain dryness and lack of smoothness, with a gray, hashy background. Compared to the AK120 it is a shade brighter sounding, and perhaps a tiny bit more resolving, but really I am not hearing anything to justify the massive price increase. The Calyx M sounds much better. More resolving, much smoother, blacker backgrounds, "bigger" sound, although a bit less three dimensional. The UI of the AK240 is better, but that is a minor issue.
Given the cost of the AK240, I was really expecting much better. I am now debating whether to spend another $500 sending it to RWA for modding, or whether I should just cut my losses on this player.