What image are you running on your Pi? I believe that with the Roon Ready image from Hifiberry, the onboard sound options are disabled.
Regardless – do not get your hopes up sending high quality audio (let alone DSD) over the Pi’s HDMI: it is primarily a video device and it’s audio drivers are severely underdeveloped and limited to 48/16.
You can get HDMI to work using Raspbian Lite or DietPi – but it will not lead to aural satisfaction.
I purchassed an additional PI3 to use it as another zone…
Configuring the new PI3 as reading the Roon on PI tutorial for beginners, I noticed that if I do not disable the PI3 on board audio as stated below… HDMI output shows as a zone on ROON CORE…
…Bad news is , but the unit can not access the WIFI dongle and connect wireless, leaving the zone to only ethernet.
My question now is… is there a way to dissable blutooth on the PI3 without dissabling all main board audio? so I can have WIFI conectivity and HDMI digital output?