This review is great and really convinced me that I want a pair of A900x. Unlike you, I'm very much a basshead and am interested in getting used to headphones with a neutral or slightly less than neutral bass response because there's so much more detail to be heard with the bass toned down. Like you, sharp, excess and harsh treble is very fatiguing to my ears and I like it smooth as possible. The ATH-A900x sounds like the ideal closed headphone at it's price.

Excellent review. Overall the A900X is a fantastic headphone. Nice detail retrieval across the entire spectrum. Like you I was finding it a bit bassy and also too trebly for my tastes. I tried layering the pads by using foam underneath the pads. Although that took care of the treble, it made it even more bassy. I finally tried your suggestion of making the opening smaller and that seems to have taken care of both issues, the bass and the treble. The change seems a lot to my liking (just hope the liking lasts .. lol .. you know how these things are). Anyway thanks for comparing these two headphones. The AKG 550 was on my radar since I was looking for a good closed session headphone. The AKG 550 sounded awesome when I tried it, but it was only briefly and not with a wide range of music. From what I have read, it seems to stumble when certain songs demand a certain frequency pitch that it can't quite handle. This has been a comment from various sources. So .. given you could only keep one of the headphones, which one would you keep for music listening .. but I guess I already know the answer to that.