I've had the opportunity to compare both 598 and X2 back to back. If you really like the bass on the X2, then you may be a little disappointed by the bass of the 598, as it tends to be more neutral to light. That said, I found the treble of the X2 a bit sharp at certain frequencies, whereas the 598 is smooth throughout. I think the 598 is the better sounding can overall, especially if you listen to slower music using real instruments and recorded with soundstage and dynamics. If you tend to listen to a lot of today's music, electronic or otherwise, that tend to have a compressed soundstage and dynamics, and is more bass-driven, then I'd say the X2 is better suited for that.
Oh, and in terms of comfort, I found the X2 to clamp a bit tightly on my large head. The 598 are very comfortable.