iTunes
MacOS Catalina (fall 2019) comes without iTunes.
Apple decided to replace it by separate apps ( Apple Music app, Apple TV app, Apple Books app, Apple Podcasts app). However, these apps still use the iTunes library.
Window users can continue to use iTunes.
The rise and fall of iTunes, Apple's most hated app - The Verge
To obtain bit perfect playback;
Disable all DSP like "Crossfade songs", "Sound Enhancer" and "Sound Check"
Disable the equalizer
If you use an outboard DAC over Toslink or USB; set volume to max
In Audio MIDI Setup match the sample rate with the sample rate of the audio.
iTunes uses a fixed sample rate.
Audio with a different sample rate is re-sampled to the setting in this panel.
If you want automatic sample rate switching you need a third party product like Bitperfect.
Source: krmathis
FLAC
Apple don’t support FLAC.
You can install Fluke to import FLAC in iTunes.
A detailed description can be found here.