No, it's not the bass. It's hard to describe why exactly, I'm still a novice in this hobby so maybe someone else could chime in on their opinion. The music I listen to is all lossless so the reason might either be due to poor mastering of the albums or that the X1 just doesn't play those songs to my taste.
I just find myself listening to other genres more because I feel they just sound much better. The acoustic rock songs I've heard through them sound great though.
What a about this kind of rock? http://www.youtube.com/watch?v=k60gyLuc0Tc