Wow, that’s an ancient device. What kind of connection is 5? If it’s a digital optical output of some type, you could potentially use an adapter to change it from that output style to TOSLINK, which would connect to the standard Sonos optical to HDMI Arc adapter. However, my hopes aren’t high on that, it implies a stereo output, not a 5.1 output, based on the devices you can connect, which suggests it’s an analog, not digital output.

The more likely option is to pull out the audio before it reaches the TV. If you just wanted Dolby Digital, a standard HDMI switch that included an optical output would work much in the same way as I suggested above. If you were after an Atmos signal, you’d need an external ARC/eARC generating device. 

There is the HD Fury Arcana, the Feintech VAX04101k, and the latest, is the OREI HDA-935. You can also order from those links from the companies directly, or check your local retailers for availability. Amazon may carry some, depending on your location.