Of course I know the XB stands for extra bass. I have the Monoprice 8323, which I feel have a pretty bassy output, but they don't lack in mids and highs. Same goes for the Panasonic RP HTF600. Powerful bass, but mids and highs aren't completely sacrificed for that bass.
Headphone Reviews and Discussion - Head-Fi.org
I'm not really sure what you were expecting from these...