Some quick straight out of the box impressions:
Well packed, heavy, very solid metal, nice build quality and appearance. I would probably replace (personally) the Phillips head screws with something sexier. Torx or socket caps plz.
My initial impression is that it sounds better than the B22 or the Phoenix. If I had any initial criticism with the HD800, I think that it's a bit aggressive, metallic, intense, maybe less sexy midrange than the B22. It's still better than the Phoenix which is harsh with HD800. But compared with B22 the Mjo has more treble detail, a slightly higher and more believable soundstage, the sound is overall more realistic, it has a lot more slam and excitement, the bass is better. At $750, people would be insane not to buy one of these before anything else. It's hardly more expensive than some portable amps. Considering that it costs $3000 to commission a new B22 and over $1000 to DIY a half decent one, you would be nuts to consider a B22 when this amp exists.
Edit: LCD3 is greatly preferable over HD800 with this amp. It's just better in every way. More natural, realistic, and just in a better balance. This is still one of the best HD800 amps, though.
I will be editing this post as new things come to me.