As a fellow tinnitus sufferer who has hearing loss (and wears hearing aides) I am interested in getting the 600s. I currently use the HD558 which is a comfortable and non fatiguing headphone. Let us know how things go with the 600s, if you get them. Do you have a sense of what it is about the T1 sound that causes the problem?
My feeling is the treble extension is the issue.
The highs just seem too penetrating.
The tinnitus is particularly effected by high violin sounds for example.