Solved
OK, I have managed to flash my Yamaha RX-V667 by ignoring the part of the Yamaha instructions that says you need to burn the .WAV file to a CD in Audio CD format.
Basically copy the .WAV file to a USB stick (FAT32 format) and plug it into the Sony BDP-S570.
Navigate to the .WAV file and prepare it for playback, but don't press play just yet.
Prepare the Yamaha RX-V667 to receive the firmware, then simply press play on the Sony BDP-S570. 14 minutes & 5 seconds later, Job Done.
Just remember, you still need to connect the BDP-S570 to the RX-V667 with an optical cable or coaxial (I used optical)
On the down side, this has not remedied what I was hoping it was going to fix.
Basically, when I turn on my FoxSat HDR, the RX-V667 does not automatically switch to it, I have to manually select the HDMI input on the remote.
This is probably a feature (or lack of one) on the FoxSat.
Does anyone else have this problem?