Optical + Auxillary Mixer

So I have an Echo Dot and an Xbox One X. I have an old Sony Surround sound system with only Optical and Coaxial inputs. I want to Echo Dot with an Auxiliary output to be mixed with the Xbox One X with an Optical output.

I've been looking for the past week but have only been able to see options for Optical and Coaxial inputs and not Auxiliary.

"auxiliary" is one of several analog, line level inputs which were all identical. CD, Tape, Tuner, etc. all used the same physical and electrical specification.

The Echo Dot also has a Bluetooth though, so you can pair it with a receiver like this:
Then connect that to your Xbox via the optical.

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