Hi Peter,
I ended up connecting the transmitter to the optical audio out from my Blu ray player, rather than fiddling around with the options on my receiver (I only have the Blu ray player hooked up to the receiver so no need to make my life more complicated than strictly necessary), *but* I did check this with Yamaha beforehand as I do occasionally want to connect other devices. I have a far older receiver than you, but perhaps the same applies. The tech rep said that the first step would be to check the audio output format on the device hooked up to the receiver, i.e. in my case I needed to make sure that the audio being output from the Blu ray player was set to PCM. However, he wasn't sure that even this would guarantee I could then plug the transmitter into the receiver for digital audio (I gather it's not a given using an HDMI connection - not sure whether this means you might also need to connect your devices to the receiver using optical cables). As I said, in the end I didn't bother, but I can see why you would want to link the phones to the receiver if you have more than one device attached...
Good luck and it would be great if you could post the solution here once you have it.
All best,
almoganga