Unfortunately I can't get to the mediafire samples from behind my company's firewall at lunch time, so I haven't listened yet. I'll try to remember to listen when I get home. As someone who owns AT853's and U853's, and a SP Battery Box and an ST9100, I'm going to prognosticate before I listen that the U853's > BB are thicker sounding compared to the AT853's > ST9100 which has a brighter high end. We'll see if I'm correct when I listen tonight, or if I'm full of shit (it's been known to happen).
In my opinion, the difference in the U vs "older style" caps is less of a difference than the battery box vs preamp. When I had my U853 miniguns I ran them at a Trey show, with ST9100 preamp for one set and battbox for the other set, and it was a distinctly audible difference. I really hate it when someone "disses" a comp because they aren't 100% scientifically comparable, but I think in this case it really is too big a variable to ignore.