I meant to mention it earlier to you tgat the ATC’s are power hungry but your amp should be fine. I drove ghe Atc Scm7 v2 to satisfying volume levels with slightly less power than you. I would have ket the scm7’s but they just didn’t have enough bass with that small driver.
either way you’ll want to upgrade your dac. A used schiit bifrost multibit can be had for $500 or a schiit gungir multibit, like what I have, can be had for $800.
Those Atc Scm 40 v2’s at $3500 is a pretty dang good deal!