@Klasw
Probably this is the first time you run Volumio on that PC as it appears that Volumio needs an additional device profile for this particular Nvidia soundcard configuration.
In case you want to test this, could you add this line to /volumio/app/plugins/audio_interface/alsa_controller/cards.json, just after the line with “HDA ATI HDMI”?
{"name": "HDA NVidia", "multidevice": true, "devices":[{"number":3, "prettyname": "HDMI 0", "defaultmixer": ""},{"number":7, "prettyname": "HDMI 1", "defaultmixer": ""},{"number":8, "prettyname": "HDMI 2", "defaultmixer": ""},{"number":9, "prettyname": "HDMI 3", "defaultmixer": ""}],"type":"integrated"},
Please let me know whether this solves your issue.