Recommendation for Digital Coax

Optical cannot handle higher resolution audio files. SPDIF can.

’spdif’ (sony philips digital interface) is a digital music data transfer format that can be transmitted/received either optically (toslink) or electrically (rca/bnc)

https://www.lindy.co.uk/spdif-connections-explained-i70

optical spdif has some bitrate limitations, yes, relative to electrical spdif

Why not optical?

plenty of reasons, the search bar above is your friend

i use 1.25 to 1.5 m length for coax/bnc terminated digital cables