Connect a HDMI cable from the HDMI 1(arc) socket on the TV to the HDMI socket on the surround sound receiver.
This will carry all 5.1 audio signals from the TV.
In the sound menu on the TV select the "Digital Audio Out" option and change it to "Bitstream"
On the Amazon Fire TV under "Display and Sound settings", set Dolby output to Dolby Digital Plus Automatic
Now anything connected to the TV will send the audio to the receiver.
Not all apps on the Amazon Fire TV will output 5.1