Amp gets things louder and it does seem to fill out better. Either way I like the docking capability and the other inputs were nifty, especially for comparing my onboard laptop audio and LG G2x headphone out to the E17 via the AUX toggle switch. The phone and E17 sounded similar, but the onboard was a bit worse. It wasn't huge, but definitely noticeable (narrower soundstage, looser bass, etc).
The amp itself gets the job done, and looks nice sitting on my desk. I did go back and test out the DT770 Pro 80 again at Guitar Center. The bass was most definitely more prominent and punchier than the DT990. But the DT990's soundstage and separation was far superior, and the DT990 was just an overall better sound in general. But man those DT770's could hit with some bass EQ'd in on that E17. I was able to get the DT990's close enough that I don't think it warranted the extra money, though. I am happy with them overall now that I've had a chance to A/B them with the DT770's.
Final setup: Fiio E17, Fiio E09K, and DT990 Pro 250. With this setup tested against my modded RX900 and onboard audio, the difference is awesome.
Some final pics (sorry for the pic quality...I'm no photographer and this was on my phone):
Edited by c00lkatz - 11/25/12 at 9:33pm