Etymotic provides a smorgasbord of eartips with the MC5s to help ensure the perfect fit. And, if you want the snuggest placement possible, there's even an optional custom-fitting service.
Where some in-ears can overdose on bass, the MC5s don't sound boomy in the slightest. They're a real contrast to the likes of the Skullcandy FIX as they promote a slightly leaner sound.
Despite being a little bass-light, one of the benefits is that bass notes don't lag. Instead, they're agile enough to bob around energetically during Michael Jackson's You Rock My World. Timing is top-drawer and there's good clarity where instruments and Jacko's vocals are concerned.