So, he had somewhere around 4-8 audio cables before? I believe Rokus have had just right and left analog cables and have relied on optical or HDMI to do many-channel audio.
He might be better off adding an HDMI audio extractor, possibly along with a more modern Roku. Caveat – extractors with many analog outputs are kind of rare too, but here’s an example that I searched up:
https://www.amazon.com/ATNEDCVH-Separator-Extractor-Compatible-Surround/dp/B0B6834NGR
He might consider a modern AVR as well. In 2008, I pulled out an old receiver – 20-30 years old – and replaced it with an HDMI AVR and I removed an unbelievable collection of old wiring and made my whole AV system so much simpler.