I've been listening to these cans for about 3 months now. I was perfectly fine with my Audio Technica ATH-M50 cans but I wanted to keep them permanently in my studio and have another pair to listen to with iPod at night. I found these in Japan while visiting my in-laws, but they're also available from Amazon. I'm not going to give a lengthy review or comparison. First of all, the ATH-M50 is not as flat as some people would have you believe. The lows are definitely boosted. By the way I use a FiiO E17 Alpen headphone amp. The mids are what sold me on the ATH-A900x. I would always have a problem trying to hear a bass guitar play anything higher than a D. Not anymore. The bass is ok but don't think you're going to enjoy these with Miami bass type of stuff. It will definitely hit but it is distorted at times. These cans are more for jazz, pop, classical, bossa nova type of music. I always skip past my hip hop stuff when listening with these. They do grow on you and I'm definitely enjoying them. All parts of music are important but when you're a producer (semi-pro) you need to be able to crisp mids and these cans deliver that. Great balance of highs and lows as well. I don't care for a lot of bass these days. As far as the headphone amplification; I switch between 6 and 12 db often. I can't make up my mind which is better. 12db was the obvious choice with the ATH-M50 but you have some options with the ATH-A900x. Cheers.
Nice impressions - thanks! I've had the AD900X's about 2-3 months myself (not sure how different they are from the A900X's), and recently got the WS99 Solid Bass headphones. I didn't think that I cared for a lot of bass these days either lol, but the quality of the WS99's bass is pretty darned addictive and pleasing to listen to. Having said that, I don't find the bass of the AD900X's to be lacking at all. Between those two headphones, I'm in a pretty happy place right now :)