I have a little device that splits audio off of HDMI outputs with full channel optical possible … or bone head stereo. Can’t remember how long, but probably over 10 yrs. Can’t imagine it was more than US$50. I needed it to split the audio and video to support an older receiver and projector.
Of course, having toslink out directly from the device is much better.
This comparison of should give you some idea of the perfromance differences between the SoCs used in the 4K+ (S905D) and the ‘V’ (S905X4) - although I am not an authority on this, and it doesn’t include the bespoke ‘O’ customisations for OSMC.