LFK, or anyone else with knowledge, is there a piece of hardware I can get that can take two optical audio inputs and merge them into a single optical audio output?

My purpose for this is wanting to play audio from multiple sources at one time. One example is playing a game on the PS4 but also wanting to use my Google Play Music playlist at the same time. Or, watching a basketball game with the TV muted/low and audio instead coming from the radio broadcast.

I know I can get a switcher to play one source or the other (and I may eventually end up settling for that), but is there a mixer or something else I can use to merge two audio inputs into a single audio output, with as little signal degradation as possible?
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