I am using the SB Touch with the Enhanced Digital Output App so it is passing files at 24/192 through its digital output to my DACs. The SBT has been measured to show that it is capable of bit perfect low jitter operation:
http://www.anedio.com/index.php/article/squeezebox_touch
IMHO it is a good measure of any USB converter to sound as good as the SBT.
The appeal to me of the U18 is its 24/192 capabilities. This gives me ability to play these files when I am away from home. I found that using the Toslink out from my computer directly to the D18 (the only way I can connect the D18 directly) did not sound as good as either the SBT/Coax out or the U18/AES/EBU out. I have not tried the Toslink out from the U18 to my DACs yet.
I can say that in my system the U18 performs flawlessly with no glitching, clicks or dropouts. The sound quality is a good as I have ever heard from my system. It operates with no apparent noise floor and does not impart any “flavor” on the music. As I spend more time with the U18 over the coming weeks I will provide further insights should anything noteworthy come up.
I hope this helps.
Edited by mrcasey - 10/12/12 at 1:50pm