[wesk05]

Also, if you don't need HD audio, consider Apple TV 4K with MrMC (Kodi fork).

Slight correction - if you do not need Atmos & DTS:X passthrough audio, consider Apple TV 4K with MrMC (Kodi fork).
Losless 7.1 LPCM audio is fine for most users.     

What PCM output formats does the ATV4K support?  Does it handle >16 bit depth and >48KHz sampling rates?

Not all PCM outputs are equal.  (For instance the Raspberry Pi is limited to max 4.0 output at 192kHz 24 bit, but does 7.1 for 96kHz 24 bit and below ISTR)  

ATV 4K only outputs 24-bit 48kHz (up to 8 channels). Higher sample rate content is downsampled, not sure what it does with 16-bit content. Likely just zero padded to 24-bit.