Hello I think you need SPDIF mini cable or also Toslink Mini for this specific use

the spdif exist in two format: Classic (90% share market) it’s squared whit 2-4 studs on the sides,

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Spdif Mini 10% market it’s if I remember well one side or maybe both are round Narrow whit a little hole inside ( similar to a jack )

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The Right one for Astro gaming mix amp are classic SPDIF.