At the DAC all digital inputs are identical: any differences in volume come from different processing upstream. If you have big perfect paths then the volumes will all be identical. Even with no effects in the paths, sometimes it’s hard to find all of the volume controls. With video players, there is often compression in the path, there may be speaker configuration settings (e.g. crossovers to a sub, speaker size adjustment, speaker distance adjustment, etc.) Perhaps folding of 5.1 (or whatever) to stereo… With broadcasters in the path there may be a lot of processing going on, including louder (or more compressed) volume for commercials which make me turn things down on the average. Movies often have more dynamic range than TV shows so they have to be quieter on average. Satellite receivers, cable boxes, etc. often have dynamic range adjustment settings… The list goes on forever. Even with simple stereo from streaming services some have their own volumes, but some share volume control with the OS, some allow a volume “above 1” (VLC, for example) so unless you can run some sort of bit perfect test you can’t tell if you have all of the volumes set to unity.