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.
I had a similar problem where I had previously used the optical output on the Apple TV to connect to a pre-amp/DAC. When I upgraded to the 4K Apple TV I connected the Apple TV directly to a Vizio 4k TV, fortunately for me my 4K TV had an optical out socket. Effectively passing HDMI audio from the TV to my pre-amp/DAC.
Another alternative I just thought of is to look into the Sony Blu-ray players.  They will have built in streaming apps for Netflix, Amazon and (I think) Hulu.  Maybe a few other services.  The upper models have digital COAX output (much better than toslink) and are highly superior streaming transports when compared to AppleTV and others.   That b big said, you cannot install any old app like you can with AppleTV or Amazon FireTV.