Peeking at the specs, the Holo May DAC outputs 2.9V for RCA and 5.8V for XLR, while the Moon 280D outputs 2V for both XLR/RCA. That may explain the lower volume level on the ARC Ref6SE. I did not see any options to trim down the output at the Holo May DAC. Given the ARC Ref6SE accommodates for 18V at XLR or 9V at RCA inputs, I don't think there's anything to worry about.Normally the volume on the ARC REF 6SE with the Moon or NAIM to listen at 80db the volume is around 34. To reach 80db with the May it varied between 24 and 28 on the 6SE.