usb to optical 5.1 audio adapter required

Hi All,

I have a 2019 iMac computer which I use for composing and arranging music. I would like to enter the world of 5.1 surround sound, and connect the computer DAW to one of my audio systems which have an optical connection, but my computer has only headphone and usb outputs available.  I think I need a usb to optical 5.1 audio adapter, but I can't find any suitable boxes on the web. Most boxes available from the pro music shops are aimed at multichannel recording, and I  already have one of those. It appears that Apple used to put out 5.1 encoded audio through an optical connector incorporated into the headphone socket, but this has been discontinued. 

Any suggestions?

Foggy