My AP001 arrived about an hour ago.
I've been using the little guy with Sansa Clip Zip and Brainwavz S0.
Its a fun little amp that's for sure and I DO hear improvements over Clip Zips headphone out. Sound enhancer / bass booster are words to describe this cute little thing. Another word that comes to mind is "FUN. The bass boost is obviously there, so throw EDM, ambient, dance music on you get a great atmosphere. It quite impressive actually what this little box does. At first I wanted turn the bass boost off, but went with it, now I'm having a ball.
Yet to try a party for two scenario. You guys are going to like it but keep in mind its purpose FUN!
I'll pop back in when I've spent some more time with AP001.