I used to be very concerned about this, and as a result purchased the $10 BitPerfect app, which sits between iTunes/Music app and the underlying MacOS, allowing on-the-fly resolution-switching (and also integer mode rather than floating-point mode, which keeps things bit-perfect). This is the major weakness of Apple's built-in core audio processing: it cannot do on-the-fly resolution switching. The padding of the bit depth is totally irrelevant - in fact, most 'bit perfect' software that claims to leave the original signal totally unaltered will still pad 16-bit (and sometimes 24-bit) content with extra zeroes to match the maximum/default/internal PCM bit-depth of the receiving DAC.

So if the Apple MIDI output resolution is set to 24/192, then everything - 16/44.1, 24/48, 24/96, 24/88.2 - will be upsampled to 192kHz, and any 16-bit source will have 8 bits' worth of zeros padded onto each PCM word to convert it to 24 bit. Not sure if you meant to type 24/192 or 24/96, but either way the Apple OS is going to convert everything to that resolution.

Amazon music app mac