"Difficult to recommend"2.5 starson by Redmist77
Pros: Excellent isolation, Clean highs
Cons: Poor bass, Overpriced, Poor durability
Summary: The Etymotic ER-6i is the second pair of canalphones that I have owned in recent years. The other pair were Creative Labs EP-630 (OEM version of Sharp MD-33.) I only paid $60 for those but I was quite happy with the sound quality.
By comparison, the ER-6i are surprisingly different. They are inserted much deeper into the ear canal which certainly gives much better isolation. It's also a lot easier to get a perfect seal.
In terms of sound quality, the ER-6is are a mixed bag. The highs are very clean and detailed though they seem slightly muted above 16kHz. The upper midrange is a tad strong but not too bad. The real area where the ER-6is fall flat is in the low frequencies. They simply do not reproduce anything that could be considered realistic bass. By contrast, my Creative EP-630s did a remarkable job of producing the type of bass you'd expect from large headphones or even high-end loudspeakers (without the visceral impact.)
Now I'm certainly not a basshead but I do like to hear the occasional drum beat. Even using some EQ doesn't help the ER-6is. I tried bumping up the low frequencies and it made virtually no difference which suggests that the single driver used in the ER-6is is almost exclusively optimized for the high frequencies and incapable of reproducing low frequencies.
In summary, my advice is to pay a bit more and get some Ultimate Ears dual driver phones or save the cash and get some Sennheiser CX300s/Sharp MD-33s.
The ER-6is are definitely not a product that can be given a blanket recommendation.