Sidssp, I'm using an Empirical Audio Freeway 2 USB to SPDIF converter, then out to an Accustic Arts Dac1 MK3. With this configuration, there is no 16 bit rate option available in the iMac's Midi settings, 24 bit only. I do have sampling rate options if 44100.0, 48000.0, 88200.0 and 96000.0 hz, I leave it at 44100.0. The Midi options will change if I put in a different dac. I don't know if it would be worth the trouble of converting audio files to a 24 bit rate before importing to iTunes, I guess I could try it and see if it makes any difference. See quote below, from bigfishaudio.com:
"What is the difference between 16 and 24 bit?
16 and 24-bit refers to the sample resolution of the included samples. 16-bit is the standard resolution of audio CD's, while 24-bit is an enhanced resolution supported by many samplers. Some Big Fish Audio libraries are produced in 24-bit, while others are in 16-bit.
It is not necessary to convert from 16-bit to 24-bit. All samplers that read 24-bit files can also read 16-bit files, and while it is technically possible to convert 16-bit files to 24-bit files, there is no increase in fidelity and therefore no advantage gained by converting in this direction."
"What is the difference between 16 and 24 bit?
16 and 24-bit refers to the sample resolution of the included samples. 16-bit is the standard resolution of audio CD's, while 24-bit is an enhanced resolution supported by many samplers. Some Big Fish Audio libraries are produced in 24-bit, while others are in 16-bit.
It is not necessary to convert from 16-bit to 24-bit. All samplers that read 24-bit files can also read 16-bit files, and while it is technically possible to convert 16-bit files to 24-bit files, there is no increase in fidelity and therefore no advantage gained by converting in this direction."