Even when listening to a recording that doesn't have much bass, like Eric Clapton's all-acoustic "Unplugged" CD, these headphones filled out the sound of Clapton's vocals, guitar, and foot tapping.
Treble detail is lacking, but on the plus side the R6i headphones reduced the grating harshness of a lot of contemporary recordings, like Arcade Fire's recent "Reflektor" album, making them more listenable.
Listening to Steven Price's rumbling score for the film "Gravity" with the($119, available for about £85 in the UK) in-ear headphones, the bass plumbed just as deep as the R6i's, but in overall clarity they far exceeded the R6i. The DX 160 iE trounced the R6i's resolution of fine detail.
The($99, available for about £99 in the UK and $109 in Australia) in-ear headphones are even more balanced-sounding, so the difference in clarity when switching between the R6i and RE-400 pairs was very significant. The blistering dynamics and immediacy of A Tribe Called Quest's "The Low End Theory" album were scaled back over the dull R6i model, so the music was less exciting. Yes, there was more bass from the R6i -- a lot more -- but by every other measure of quality the RE-400 and Beyerdynamic DX 160 iE R6i headphones were better.
The Klipsch R6i in-ear headphones are the kind that some people -- namely those who like a lot of bass -- are going to really like, and others aren't.
If you listen to a lot of hip-hop or techno (and variations of those genres) and are looking for comfortable in-ear headphones with very plump bass, the R6i will certainly fit the bill. But for those in search of more balanced, detailed sound, the R6i headphones won't be a match.