Big Ringworld fan here

Huge ending - what a tale
Correction: AVR is a SONY STR DE598.
Converter is now hooked up and I have an image. Computer says "no audio playback devices are connected." Converter is set to pass.
"Have you tried using the rca outputs from the hdmi converter to any of the avr inputs? "
The converter only has two RCA input ports. Red and White. The Composite cable has Red, Blue and Green - so not sure how to properly connect them.
The T.V. Input screen shows both an HDMI connection and an AV connection but I only get image from HDMI.
"You might need to confirm the assignment in the Sony for the optical input for the "video" audio input, but one of those Video selections should yield audio if the converter works correctly." Understanding the front is my second challenge.
1) There are "assignment" RCA ports in the back. Is that what you're referring to?
2) Optical input (at the front of the AVR) is set by using DVD, MD/TAPE and SA-CD/CD. I've sorted through them with no results (but the connections could have been wrong.