I have listened to both the XD-01 and X1, xDuoo sent both of them to me for review purpose. Also having Hisound N1 in hand now.
Full review should be posted up soon, but I will share some of the impression at here.
First of all, those who think XD-01 will be a miracle might get disappointed. For sound quality purpose I will not recommended this over Audinst HUD-mx2, O2/ODAC and iFi iDAC. In my honest opinion.
XD-01 has some very powerful driving capability for such a small box, and it is wisely build, solid and tough, mechanism seems nicely done. I turning the volume to less than 9 O'clock (Low gain Mode) will give me good listening volume already (Tested with Thinksound MS01, Perfect Sound S101, Shure Se425, Klipsch S4II and X7i), however the soundstage is quite narrow with some mediorce bass response. The only thing that seemed can keep up with the competitor is the vocal performance, but others than that, not worth for a serious thought especially when you do not need the extra features of it. However, I don't have chance to test the UA-05, which seemed promising at the moment. UA-05 should be a better competitor for ODAC/O2, iDAC and the MX2.
X1 is a good music player, which do emphasize lower region, midrange and treble seems reasonable good especially considering the price, I will say X1 is better than lets say the similar Hippo Biscuit, which often sounded dry and lacking bass body.
N1 however is a different sound tuning music player as X1, is a good and beautiful player that has small but enough for IEM driving power (Hisound told me N1 specifically made for IEM), and a gentle sound. I played some soulful and touching love songs with N1, it makes me feel like wanna cry, however, I can't scan Wav files in my N1, this is really strange.