I've had my Petite for about a week now and boy is it good!
The bass control is pretty darn good, the extension that it gives my Shure e4c's is awsome. The Shures have always been very accurate phones in the the mids and highs, but the Petite cleans them up even more.
I'm hearing things now that I could never make out before just using the ipod and e4 combo by itself. I'm also listening at lower volumes and getting more depth and emotion from the music than I ever have. This is a wonderful little amp for the money!