I can assure you, the T90 is SO easy to drive, The pretty much only thing an Amp will do for you is: Louder. Really, don't know a headphone thats easier to drive at that pricepoint.
So: If its loud enough, you probably won't notice more than a few % difference in soundquality.
For me, i am using my Asus Phoebus for it, and i honestly doubt that i will hear ANY difference to a 500€ amp.
Take the 120€ Shiit Vali (tube amp will be a nice combination to the T90) and...