You know, I'm not aware if everyone is knowledgable with this tweak/setting to do when running the USB DAC, but for Mac's when you reach into the settings of "Audio MIDI Setup" the output settings should reflect like the picture below to prevent the signal from being scaled by OSX. After making that small change, it's made a giant difference for me where the sound is a whole heap cleaner.

On another note, is it safe to plug the tube in after having turned the DAC unit on? I'm not sure, but the past few days I've been experiencing again the issue of the usb dac not working with the mac again, but just now I decided to unplug the tube and turn the unit on. Immediately that got the dac recognized in the sound preferences, but I can't be 100% certain this is the method to go on, as previously I had a back up drive plugged into a the USB at the back and it was a suspicion of mine that the drive was hogging the USB power so the bus wasn't reading the dac. When/if the usb dac decides to not work again, I'll be sure to plug in the back up drive and then test my theory out again. Until then, I get to enjoy music again with the T1 and I've learned a little thing about the audio setup aspect :)