Finally got the chance to try out the 600ohms. Very sibilant. With the Aune T1 with stock tube (which came in last wk), you must be careful not to set the volume of the source media player too loud and control the volume from the Aune volume pot to avoid distortion. Hiss is easier to hear than on my other phones (Senn HD598) - this is kind of annoying. I'm not sure if this is a shortcoming of the Aune, or of the 'phones.
I suppose I should let them burn in a bit more. What do other people think?