I'm wondering if you heard back from PrivateDivision at all? I got the below reply which seems a little generic and doesn't seem to acknowledge that the email I submitted already indicated that I am indeed connected via Toslink. It was literally word for word in my email, but anyway.
Thanks for writing in and I'm sorry to hear that you're unable to hear the audio in The Outer Worlds with your 5.1 surround system.
We don't have a lot of data about issues involving 5.1 surround sound system, so I can't promise that we'll be able to help, but let's see if there's anything that we can do for you.
Do you use an AVR or is your soundbar connected directly to your computer? Normally you should be able to make this work using 5.1 with Dolby Digital, so long as you're connected via Toslink.
Here's a few things you can try:
1. Make sure that your audio drivers are fully up-to-date. You can visit your motherboard or sound card maker's website to download the latest driver.
2. Open the Speakers' Properties through the sound panel in Windows. In the Advanced tab, you can try using a different format, and disabling or enabling the Exclusive Mode ("Allow applications to take exclusive control of this device" and "Give exclusive mode applications priority") to see if that might help.
3. A bit of a stretch, but we can also check for possible software conflict using Windows' Clean Boot mode: https://support.microsoft.com/en-us/help/929135/how-to-perform-a-clean-boot-in-windows
Hopefully this helps."
Considering my set up already works in 5.1 Dolby Digital for other applications, I'm not sure any of the above will assist, but thought I'd share it here anyway. I'll give those steps a try too.