@m669326
the musical fidelity a308 should be fine in terms of power output, it should also match well with the atc scm40 sonically as the a308 treble is slightly rolled off with no grain... with atc’s what one is most afraid of is 'classic' solid state sonic artifacts of sibilance, grain and leanness of tone, which the atc’s will neither hide or beautify
the importance of source quality feeding the atc’s is high as well, not just the amp... digital distortion artifacts will also be played through... i don’t know that $400 dac you have... there are good ones and there are bad ones... generally speaking, one of the slightly warmer sounding dacs would mate better with the a308 ---> atc 40 system you are assembling...
good luck have fun