The brightness could be due to the cabling or the source. I was using Mac Mini 2010 and I need to turn down the treble a lot for many tracks in my library. I did change the USB cable to a better one (don't need to pay for those insanely priced $1K type of cable) and the treble peakiness is reduced somewhat. Then I switched to my 2008 MacBook and the sound improved further, more balanced & less peaky. Also, if you are using iTunes, you may want to switch off the EQ. Some tracks actually sound much better without EQ.
If you are not listening at high volume, the Beyer sounds great, dark background & transparent mids. But if you are listening at high volume, like me, yes, T1 can sound unbearably bright. Especially so, if paired with bright system like Bifrost/Asgard 2, which I have come to conclude is designed & tuned for Orthos like Audeezs (those are very hard to drive especially the highs). I am looking for a DAC/Amp replacement soon.
It did sound a little bright to me in stock mode. I changed the cable for a OCC copper cable and I also mainly use it with my Woo but even with m,y V200 I personally don't think sound bright anymore and really like them.
Yes, different tubes have different sound characteristics that is why tube rolling is so much fun.
Interesting... Copper cables usually do sound darker, a bit warmer, but they don't have the same amount of details like silver ones. I read somewhere that T1s stock cable is quite a good one, although I don't know what is it's made of. Anyone has some details about that?
What type of cable did you use for replacement? Any suggestions?