Just got my X2 in the mail today and here are my initial impressions:
My set of x2s just came in the mail today, thank you Prime as always! Initial impressions, the build quality is top notch. The slight drawback to the high build quality is the weight. They are heavier, but I do not find them to be a problem, as of yet. I'm not a big fan of the sling headband. The clamp force feels... light compared to my HD650s out of the box, granted that is more of an extreme case with higher than normal clamp force. Packaging is normal, and I like the cable. I wish it would have been a 1/4 plug instead of the 1/8, but not a deal breaker since it comes with an adapter. I just got the HD650 a few months ago, leading me to essentially put away my other headphones (2x DT770, Momentum on ear (mainly for travel)). I will compare mainly to the HD650s, with maybe small references to the other cans.
Currently my source is computer wav files to Peachtree DAC iTx, to Asguard 2, to the X2. Initial sounds are pretty close to the HD650s. Most noticeable difference is the bottom end and mid range. The bottom end is longer, stronger, but muddier (hopefully burn in will cure from what I've been reading). The mid range seems more recessed, like the voice is not in your face as much as the HD650. With such an impressive bottom end, I put on Bassgasm. Much to my surprise, the phone kept up and was able to extend and produce the low notes. Very impressed. Compared to the HD650s, they struggled more and didn't have as much 'punch' or extension. The highs are accurate, but not as crisp as the HD650s or as forward.
I had to run out and meet a few guys for basketball, leaving my X2 to play while I was gone. After about 3 hours of burn in, and a shower, I feel the sound overall is a BIT smoother. I will give it more time and compare it to the HD650 more to see how the sound may or may not change over time. I so far like the X2s a lot, but that may be swayed by the delicious bass. Another big thing is that the sound leaks a lot more than the HD650s.
Currently, my thought is that between the HD650s and the X2s, the difference is small. Cost wise I paid exactly the same for both cans, which is interesting since I got the 650s when they dropped to the 319 price. Do these cans compliment each other? Should I get rid of one and if so which one? I think I'll give the X2 a few weeks to make a final decision.
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some slight changes in numbers may occur over time (though they are mostly stable)... 
