It seems for whatever reason Accuphase has implemented the DAC 60 card to operate with a low voltage output. I have to give them benefit of the doubt and assume it’s for a good reason.
I don't know, but to me it sounds like something isn't working correctly. One of the Accuphase dealers should comment if your experience is "normal" or if something is broken. Someone must own your amp with the DAC card and hopefully will chime in.
I hope you sort all this out. Are all the DAC 60 cards the same regardless of what countries markets they are built for?