I grew up in England and I don't know if it is the same in other countries but but I remember that system matching is so important and that is what I have done with my set up. The T5P's are very clear an open window on to what is being given them.
I like this in loudspeakers and headphones. What I do then is select amplification that allows that to shine but also balances it out with warmth and emotion and for me my preference is this way around rather than an analytical amp with warm speakers or headphones. Not saying my way is right and the other ways are wrong, just that it was how it was taught to me as a child learning about HiFi and I like doing it that way.
So I would rather tune in some warmth with tubes.
I think this is the most important reason the T5P's are so maligned, they are fed either inferior files, source or amp and they won't take prisoners. However, feed them a good source/amp or ideally both and they are for me the best headphones I have used in over 33 years of headphone listening as they are supremely faithful to what they are fed.
I think that is why I love Wilson speakers, they are very very similar in that respect.
So the balance for me is a warmer tube to underpin and then the more airy tube in the gain stage to give sparkle and life. But as you point out GG, with headphones that are warmer that would not be a good choice. For instance when I had the LCD's I much preferred the radiotechnique in the DL section and Lorenz or Siemens in the DF section.