I've been curious about the X1 myself, but the reviews stating they're bass heavy sorta made me lose interest. Plus, I don't think I could bring myself to buy the X1 over my favorite headphone which also happens to be around the same price; the HD650. But I think you're on that right track. If you've already heard either the AD700 or AD900, there really isn't a point to feeding your curiosity and buying the AD900X; unless you *really* loved their sound and wanted a slight upgrade/sidestep.
I too, am extremely glad Sony revived the F1. Hopefully, they'll decide to take it one step further, and make the MA1000 or something. If they made it with significantly better build and fine tuned the sound a bit more, I honestly think we'd have a simply outstanding headphone on our hands. But until then, the MA900 will do. I just hope it gains a bit of popularity so Sony has an incentive. Everyone seems to get too caught up with FOTM items, and sometimes glance over gems like itself.
Q701 is one of my favorite headphones. Unfortunately, It was quite a spacing from when I owned it and the MA900. All I can really attest to is that the MA900 has much smoother/polite treble.
Yes, there is a fine line between a fun amount of bass and an annoying amount of bass. I'm not sure which of those the X1 leans towards. I really dig the design though: open with big delicious velour earpads. I've read positive things about it's soundstage too.
Ad700s were my first real "audiophile" headphone, and I loved and held onto them for a long time. I even modded them a few times (both inside and out). My favorite thing about the AD700s was the massive soundstage and the air. The serious lack of bass eventually wore on me though. AD900s improved the bass slightly (but not that much), but also lost some of the magic of the AD700s soundstage - so I didn't keep them around. I imagine the AD900X will fare similarly.
I always thought you couldn't have an open headphone with BOTH a large and impressive soundstage AND a thick punchy sound - until I heard the Q701s. After that I knew I could never go back to the AD700s empty "tin can" bass, so I had to sell them.
Edited by chicolom - 4/25/13 at 9:28pm