wax would tend to affect the rest of the signal more than the low end(like a damping filter would do). the low end would change most from a problem with getting the right seal. but if jotpilot has already tried other tips to improve the seal, then IDK.
the bass setting affects the really low frequencies, maybe try a 50hz tone and change the bass setting from min to max, to find out if you notice a difference(try each ear alone, maybe only one ear has a problem, be it fit and good seal or actual technical problem).
check that you have turned both sides in the right direction(both clockwise or both counter clockwise), that was counter intuitive for me at first. if you don't notice the increase at 50hz. maybe the bass port is blocked(dirt or whatever), that would be like having the tape mod, the low end is at it's strongest, but the 100hz-300hz area ends up below what the IEM usually do by 2 or 3db if I remember correctly. might be what you're experiencing? or just that you remembered them as stronger in bass than they are?
as there is a mechanical design and it's rather a small vent, I imagine you would need to send the IE80 to sennheiser to get it cleaned/fixed.