There is a 5 or 6?
I bought a used miniIV with ad8397s and love it. The battery is just about long enough ~8 hours and the sound is top notch. It is also so small that it doesn't fell like having an amp at all. Had loads of juice to drive full sized cans especially with the 5.5volt boost switch on. The extra features work well enough that I don't consider them "extra" but actual valid features, for example the bass boost adds very little distortion (almost as well as the sharp md players in this respect). The crossfeed is nice to have (though still more like the meier/hr in performance, unlike the minibox-E's circuit which sounds more like a dsp solution), and the p->s impedance switch and gain switch are essentials. All this shebang for 150 used is quite a bargain.
I wouldn't buy new or send anything in for "upgrades" though, as lately the xin line has caved in to the "knowledge" (personal preferences) of quite a few annoying people so the sound has been floating more and more towards the supermicro in signature, for example the latest supermini IV 4/12 updates as well as the xin Reference amp.
The micro isn't the best in sq, but since the "popular" guys on that other place praise it as a godsend, xin now focuses on the "warm fet" or whatever sound those few "influential" people like because the ignorant masses there are mere flocks agreeing with the popularly influential and most likely highly dumb few.