I never try one, from what I have read Sennheiser HD251-II is more towards to quality bass than quantity bass. This doesn't mean they are lacking bass, they have plenty and hit hard. If the bass you like is something 'bloated', then Sennheiser HD251-II is not suitable for you :)
EDIT: If budget is not a problem, have a look at Edition 8.
Edited by KLS - 6/2/10 at 10:45pm