I have the T1 on my AKG K550 at work, and it sounds great!
The big hazard about the T1 is tube rolling. Most people will say it is an advantage but I say its a hazard.:wink_face: It can cost you a lot because it is addictive! just look at the T1 thread
http://www.head-fi.org/t/633006/aune-t1-usb-tube-dac-amp-discussion-thread-see-first-post-for-faq
If you don't watch your self you will soon be sitting with a bunch of expensive vintage tubes which has a negligible sound variation.(my opinion). I have a few tubes which is not expensive, but from time to time i wander off into eBay looking for that mint condition Amerex ecc188 gold or a rare Siemens Ecc...
If you buy a T1, buy a russinan Voshod 6n23p which is cheap, easy to get hold of and pair great with AKG sound signature (warms up a little), and then, NEVER LOOK AT TUBES AGAIN!!! (but most likely, you will fall...)
I actually wonder about changing my T1 with a Vali + Modi, becuase it has soldered tubes, which hopefully will cure me.