I do not believe the fibre optic cable is the culprit for the volume limited TOSLINK input…
(I have had many TV/theatre installs where for whatever reason, things didn’t work as they should, until we power cycled the TV set- not saying this is the solution, just that I agree that it doesn’t sound like things are acting ‘as they should’)
Regarding the 3.5mm feed, so long as it isn’t obviously hissy, nothing wrong with using it…
If the TV was a high price point part, and ‘from a bygone era’ (not built in the last four years) it probbly has an AKM DAC chip/something not ESS based…
using parts built for ‘music first’ (not spec sheet brilliance) might mean its’ sound output was inline with consumer expectations and was sufficient…
if not hissy or distoring, by all means continue to use the 3.5mm feed - you may wish to line level the 3.5mm input so that the TVs volume button doesn’t alter the signal, OR set the volume to match other inputs on the Muso (so swapping inputs equals roughly equal volume levels), and then stick with using hte Muso volume control for ALL volume adjustments.
getting back to the TOSLINK- obviously the TV needs be set to PCM (pulse code modulation/aka “2 channel audio” in the case of TVs (Playstation and Switch consoles will happlily give multichannel PCM but requires HDMI))…
do not leave digital output set to Auto/surround… (PCM is correct)
maybe look at any menu options that removes volume adjustment on the TV side… (apols I have handed on my last couple of Sony TVs, and the Sony projector I used doesn’t do audio, so is missing the requisite menus.)
perhaps share the TV model… (or a link to the manual, please)…
thanks in advance.
(not likely the TOSLINK cable, and ‘fine to use the 3.5mm feed’)