Add an attenuator (passive pre) to the fixed level output (ahead of the amp) and you should be good to. I used to take the coax digital signal from my Music server and run it into a dac and then on into the pre in my main system. At the same time, I also ran the analog out into a Sonos Zone Player for distributed audio. I never had a problem....but both chains (main system and Sonos distributed) allowed attenuation.
Good luck
Marty
Good luck
Marty