I know this is an old post, but I thought I'd chime in. I downloaded the Big Bang Universal demo. The instructions for loading it aren't all that clear, as there doesn't seem to be a stand alone player/interface. Only by opening Reaper did the Big Bang window pop up, requiring an iLok account. Okay, no problem, it's a demo. So I did that and loaded a Virtual instrument onto a track. I had to really tinker with the Audio and midi setting to get any sound out, and to be sure I was getting ANY sound, I loaded my AD2 on another track. That works perfectly. Eventually I was able to get some rudimentary sounds out of Bang, but the maps were all over the place. All the pads played the same voice. I tried the "learn" button, but that was not a clear path to victory. Perhaps I was spoiled by demo-ing EZ Drummer and finally purchasing AD2, which installed and works quite well. Big Bang seems to be a half though out concept, though the myriad files that I downloaded (9 gb worth) are named like things I'd like to hear. Not sure how to get them to respond to my trigger assignments.
I tried the Midi learn button, and all it did was open my Finder window so I could point it to...something. Perhaps it's making me build everything from the ground up thereby offering me full-on customization and features. Perhaps AD2 made things too easy on me and I'm playing things that shouldn't exist. However, since Sonivox is owned by Inmusic (owner of Alesis), I assume Big Bang has a broken wire or solder joint somewhere!
I might play around with it a little bit more to see what it truly does, but I'm not sure it's worth the time to get it working better than AD2 (which rocks so far).
Anyway, that's my newbie, uneducated review of my experience with Big Bang Universal so far.