I don't have an E17 (Yet), So i can't comment on it's sound.
It has a digital volume control so you push up/down buttons instead of turning a knob. Some people don't like digital volume controls.
It is a DAC+amp when hooking up to USB / S/PDIF / Coax, or just an amp when hooking up AUX Line In. If you are going to connect this up to your computer as well to use it as a DAC, then this is a feature the E11 does not have as it's just an amp.
There is a massive thread with a lot more info on the E17 here
All questions should be answered there if you care to sift through the 240+ pages :)
E17's were backordered from quite a few places a while back so finding one might take some time.
There are quite a few other amps that sound better than the E11 or E17 but the pricing scales up pretty quickly.
Here is an excellent review of 7 sub $100 amps
And here is an older thread with 11 portable amps compared ranging from $129 to $699
Much info to chew through. :)