I don't know why people insist but... the M100 DOES NOT, I repeat DOES NOT NEED AMPING!!! Now that we got that out of the way, of course as with MOST headphones, the M100s will BENEFIT from an amp but it doesn't really need it!
Regarding bass and sub-bass, if the song has it, the M100s can reproduce it. Simple. You don't need the ZO2, or a cmoyBB/c421 with bass boost, or a Fiio with bass boost, etc. These I already find are "bassy" headphones (mid bass is a bit pronounced... just like the Denon D600s...).
Personally, I find the bass to be "enough" and has a good amount of sub-bass to feel those lower notes. Tracks like Kaskade's Fire in your New Shoes, Skrillex Amplifire, Deadmau5 Ghost's n Stuff, Strobe, Three Six Mafia, etc. sound mighty fine to me. More bass would probably hurt these m100s...
but IF YOU ARE A BASSHEAD, and want to always feel your head vibrating and the drivers going to max while unscrewing the enclosures, then muddy the sound up by buying a ZO and increase the bass till your heart's content!
Or better yet, there are other, cheaper, options for getting the same effect and good sound quality (i.e. M-Audio).
Thanks.
Enjoy.