OK...that's a really old receiver, and it does not output HDMI audio sources, only passes them through to the TV. Also, that TV will not send HDMI audio out over optical, and neither support HDMI ARC, so you have two options here. One, get a new receiver which will output the audio directly (pretty much all new receivers will), or two, get an HDMI audio extractor which will take the audio stream from the Fire Stick and output it separately over optical or RCA. You'd then run that audio to either the optical in or RCA in on the receiver.
https://www.amazon.com/J-Tech-Digital-Extractor-Converter-JTDAT5CH/dp/B00BIQER0E/