MC will automatically pad playing audio to the max bit-depth your DAC supports on-the-fly by adding zeros (it's not doing any sort of dithering). I suppose it could depend on drivers on stuff, but for me with the various DACs I've used the max has always been 32-bit on both Windows and Linux (and macOS in the past).
I 'm referring to the input not the output of audio path pop-up message. The input should display this: 48 kHz 24 bit 6ch from Source format truhd for the above example(highlighted in Standard view). Please note for 16bit audio depth , it correctly reports as 16 bit.