Setting up Home Theater with AppleTv4

Hello - Just when I thought I knew a thing or two, I don’t! If anyone can give me some advice I’d really appreciate it. I replaced my first generation Apple TV with #4. Of course it’s now apples and oranges, no pun. Gen one Apple TV had an optical cable that connected to the sound system. Gen 4 eliminated optical and utilizes USB-c. I’m connecting to an older Harmon Kardon HVR 140, which uses the very old fashioned white, yellow and red cable connectors, or optical.

I purchased a cable that has three plugs (red, white yellow) on one end and USB on the other and an adapter to convert USB to USB-c. It should all work, and it doesn’t. Anyone familiar with Harmon Kardon - I’ve plugged the Apple TV to Video 2 Audio/Video input. Any Brainiacs available? I’m stumped.