Digital converter - Optical to phono - Random question

Hi All,

I know this might be a bit of a long shot but I've got an old 5.1 surround system that uses phono as front left/ front right, cent,sub, rear left/ rear right.

And now I'm upgrading most of my computers and Monitors to HD as I work as a Freelancer Sound, Camera, Editor.

I'm looking for a digital converter that would take one optical digital line and convert it to an analogue 5.1 phono or jack.

So it would go

IN - Digital optical

Digital to Analogue converter

OUT - Phono/Jack - FL/FR
Phono/Jack - C/S
Phono/Jack - RL/RL

Just wondering if anyone knows of any kind of contraption/ gadget?

All messages would be greatfuly appreciated.