So...it did combine them or it didn't? 24/192 and 16/44 are playing on your computer - what do you send to the DAC?I think this is why audio drivers have audio managing programs. They ensure this doesn't happen. With Deadbeef there used to be an option to tell ALSA to release the plugin resonsible for the audio playing on the music player and transfer the management to whatever plugin in, or core that managed combined video and audio for example. It used to be audio at 16/48 from what I recall.
Look at it from the DAC's point of view. It doesn't care what the OS/driver/apps do. It just wants a stream of a given depth/rate to play.I'm fairly certain that a sound manager doesn't try to combine the bit depths and frequencies.