Trying to decide between the T1 and HD800. Which one wpuld handle prog, power, and folk metal best?
Hey, welcome to the thread!
In almost every scenario the T1 is an iffy and unquestionably overpriced headphone. I owned it, and I really wouldn't recommend it for metal at all. It has weak, weak impact on all but a very small number of amps and it lacks the textual microdynamics to give you a strong rhythmic connection to the music. If you're checking it out because you read it was good for metal on Headfonia's T1 vs. HD800 showdown, I'll tell you that observation was completely off base on their part and it wasted a lot of people's money (including my own).
The HD800 is much better in pretty much every way, but, as I'm sure you know, it is extremely finicky with the audio chain - you can hear the effects of not only your amp and DAC, but your RCA cables, power cables, headphone cable... everything. It can be a little bit harsh with the wrong chain, but with the right equipment, it is absolutely sublime. So between the two, I'd pick that one... but there are many other options available that are even better for metal that are worth considering such as the MrSpeakers ETHER and ÆON, the Hifiman HE-6, the ZMF Atticus and Eikon, and a couple of Stax models.
We tend to be a pretty helpful bunch in this thread, so if you could enlighten us to your budget and the other equipment in your audio chain, we'll make sure you end up with something you really like.