The X1 wins hands down. It has a nice extended bass and trebles that don't get strident. Soundstage and instrument separation is beautifully done. It plays all genres of music, everything from from classical to EDM, very well. Never congested, always smooth and lots of fun. That said, these things can't really be worn outside because of the open back design. It leaks sound like crazy, they're like little loudspeakers and don't they don't isolate well either.
The Amperior is nice little headphone with a very fun in your face sound and a hard hitting bass but it can too in your face sometimes. When it tries to do too much the sound gets muddled. The trebles can also get really strident on certain recordings. But for most of the stuff I listen to, not Maria Callas
, it's great. That in your face sound makes is so fun and addictive. They are a steal at their current prices. Get'em while they're hot!