I'm considering purchasing either the T1 or HD 800, and in the past few days have tried them both (listening sessions were 2 days apart, so my ears may have been in different shape, but I referenced them with new HD 600's, the same laptop/playlist/amp [not sure about exact listening volume], and made notes on my impressions at the time of listening). The T1 was brand new, straight out of the box, and the HD 800 were a demo pair with approx. 50-100 hours of listening time.
To me, the T1 and HD 800 are slightly treble-centric headphones. I found the T1's treble to be more brightly 'hot' than the HD 800 in certain places e.g. John Coltrane's sax on Resolution (John Coltrane's A Love Supreme), and the trumpets on Led Zeppelin's Kashmir - on the T1 the Coltrane's sax was quite piercing to the point of being ever-so-slightly uncomfortable and shrill, making me turn away, and trumpets on Kashmir sounded nicely raspy. On the HD 800, the same sounds came across as less bright (Coltrane's sax was less piercing) and overall I find the HD 800 to be a warmer headphone, especially on the low-end - maybe that low-end 'boominess' balanced out the treble peak, and maybe the frequency of Coltrane's sax on Resolution suited the HD 800 better. I'm finding the differences between the T1 and HD 800 quite slight and very subjective. That the T1 I tried were brand new the HD 800 had been used probably affected the sound too.
Just wondering, do any T1 or HD800 owners use EQ to compensate for the treble-centric nature of these headphones?