Interesting discussion going on another board ... apparently Windows built in Media Player's volume control is considered lossy, in that it enables an addon to digitally reprocess the data stream - that addon is otherwise bypassed when the volume is all the way up. Same apparently holds true if the master volume setting isn't also defeated by leaving it up all the way.
Not sure if that's specific to DirectSound or WASAPI, both or neither. Don't know how much truth there is to that as it doesn't seem to be a well documented "feature", but makes me wonder about MC's internal volume controls?
PS ... I don't use Windows media player, and I do already leave the system volume all the way up, but I DO use the MC volume setting to tweak playback as needed - too lazy to use the analog controls available on my system. MC's internal volume is usually at 93%, but varies from 85% - 100% depending on the album selection.