I use Mark Grant glass core cables and find they do a great job. Stan also sells THIS cable which looks very similar to the Mark Grant cables.
They're both very high quality multi-fibre cables that are vastly superior to the single core plastic crap that most commercial Toslink cables are made of.
Source: Apple TV 4K - DAC: Beresford Bushmaster Mk II - Preamp: CI AudioPLC-1 Mk II - Power Amps: Musical Fidelity 550K mono blocks - Speakers: Wharfedale Opus 3 - Cables: Mark Grant etc - Misc: Belkin PF30 mains filters.