You know my take on these phones and that was with the old BH which is more or less the same. It is hard to blame the amp for making the phones bright though when it is essentially dead neutral. The ES-1 as Mikhail built it is duller then a stack of wet towels and I'm sure Justin went a similar way with the Aristaeus as Senn did with the HEV90, tone it down a bit to make it sound beautiful but not true. When I moved from the SR-007 to the SR-404LE on the T2 it was clearly too bright but that's because the phones are on the brighter side of neutral. This is with the APL as a source which has a transformer coupled tube output, nothing like the slightly sterile and bright Esoteric sound.
I loved the SR-Omega from my old BH but the upper midrange/treble issues were still there. The amp didn't try to hide them in any way but other parts of spectrum were good enough for me to ignore it. That said you could be happier with an AC coupled amp. I would also look into different cables, ones that aren't trying to sound impressive.