It sounds great to me. My last amp/DAC was the $850 HeadRoom desktop amp/DAC. This obviously isn't technically in quite the same league, but I honestly am just as happy with my E17 now, of course I've never heard the same headphone with both or compared side by side. I'm sure the hardware inside the HeadRoom is much superior. I've never compared the two side by side, since I sold the HeadRoom amp/DAC well over a year ago and got the E17 3 months ago. I guess what I am trying to say, is that I am not disappointed with the little E17, after using the much more expensive HeadRoom amp/DAC in the past.
Everybody has to realize that with this hobby, especially with amps and DACs, is that the rule of diminishing returns kicks in pretty hard. An amp or DAC that costs 5 times as much, won't sound 5 times better, it would be more like 10-20% better if you are lucky. Of course saying 5 times better or 20% better is just as useless to say because these things can't be measured like that anyway. If you're happy with the E17, live and listen happily.