Nathan ask Glenn for Llundal transformers which are a step up, but they cost a lot more.
A lot will depend on your tube choice regarding sensitive headphones the 6336 will be the best bet.
I never tried my ATH W5000 yet with my tube amps they are hooked on a AT-HA5000 (Raffinato set) SS amp.
I am very pleased with the audio transformers Glenn has used in my amps.
Some pre-midnight thoughts for you.