I'm not sure whether any Sennheiser would satisfy a basshead. I haven't heard the HD518 and I've read it's on the warm/bassy side, but we're still talking about the same driver that goes into the HD558... and that is hardly bassy at all.
Anyone else care to comment on the bass of the HD518?
Also, they are open, so they will leak music. Might not be the best choice for school.