And how about midrange & treble transparency? Is it better than the XTRA? (keep in mind that I don't believe much myself in long burn-ins of amps/sources/etc.)
The treble and midrange of the XTRA black is very nice. Highs are extended and mids are not in your face but smooth and natural. For the money this is a tremendous amp. I have the LD M+ and they are nothing at all alike. The XTRA has some real circuitry and about 20 times the parts. You can even change the battery because it plugs in but on the LD it is soldered into place. The bass on the XTRA is much stronger and integrated than on the LD. The XTRA could sell for much more. You need to let it burn in, oh sorry, get used to you and like you to give its all. :^)
The Micro Tube is separating the vocals and instruments more and not congesting as it ages and learns what to do. I can hear more separation with the Micro tube over the XTRA but I could easily live with the XTRA and not worry. I will have the Xin IV shortly and will give the XTRA a real run for the money on the comparison.