I bought a McIntosh MC225 integrated vintage tube amp with upgraded MC240 transformer/ new tubes and full clean up.
I initially felt like selling my mjolnir but it's useful to have. The McIntosh simply outperformed my HE-6/HD800/LCD-3's through the gung/mjolni/bha-1, vintage sansui and marantz.
From what I can tell push-pull like your MC225 is the best route for tube amplified HE6's, the only SET I've found that on paper has the voltage swing required for HE6's is the Audio Note SET. Hopefully Hifiman will come out with a new flagship with sensitivity too at least work with a 300 SET. Until then I think I will stick with my HE-500's as I am a bit of an SET devotee.