The E17 is what I use right now and I like it a lot.
In the past I've owned the big $850 HeadRoom desktop amp/DAC. It's the only other DAC or headphone amp that I've had and I'd say that it's obviously technically better than the E17, but I am perfectly happy with my E17. I had the HD650 and said HeadRoom amp/DAC, but due to monetary issues I had to sell them off to pay some bills. A few months later when I was financially stable again I had to have a good full size headphone once again, so I figured I'd try the Q701 and the little E17. I've now had the Q701 and the E17 since October. I'm sure it's mostly the headphones fault, but I prefer this Q701 and E17 combo to the HD650 and HeadRoom amp/DAC.
I also have been playing with a Fostex T50rp lately. The way I currently have them tuned they sound alot like the way I remember the HD650 sounding, but with better bass extension, and maybe slightly more bass overall. Same great mids, and same smooth gently rolled off treble. Anyway, they also sound great with the E17.
I started with the E17, my first DAC. Now, the Gamma2, and never think about going back
This hobby is a money pit. Especially since I will never be able to sell my K340, K240 Sextett, or Q701. Since they are so awesome.