Get >1.5m or <1ft (I can explain why). It applies only to coax. It is a system thing - a cable that sounds great in one system might sound bad in another (characteristic impedance mismatch and/or electrical noise induced jitter).
Cable adds time jitter, that converts to noise on analog side. This noise is proportional to loudness and undetectable without signal. It affects clarity, timbre, imaging etc. It can also produce unpleasant sibilants (or shrill).
Toslink connection (any distance) does not need matching and is not sensitive to ambient electrical noise, but is sensitive to system noise since transitions are slow (slow transitions thru noisy threshold = jitter). Toslink does not create ground loops. You have to try different coaxes and Toslinks it in your system in your room. Recommendation means nothing.
Cable adds time jitter, that converts to noise on analog side. This noise is proportional to loudness and undetectable without signal. It affects clarity, timbre, imaging etc. It can also produce unpleasant sibilants (or shrill).
Toslink connection (any distance) does not need matching and is not sensitive to ambient electrical noise, but is sensitive to system noise since transitions are slow (slow transitions thru noisy threshold = jitter). Toslink does not create ground loops. You have to try different coaxes and Toslinks it in your system in your room. Recommendation means nothing.