Wireless Sony AV Receiver won't connect to my iMac

Good evening Duane, really appreciated, however, I wish to play my iTunes, iPhone music through my Sony AV Wireless Receiver STR DN840 and speakers.

I had it connected for a couple of years, but disconnected while painting the room and now the AIRPLAY icon on the iMac will not show the SONY Receiver, only the iMac computer. The iMac is 4 years old, however it work in the past. Just wondering why it won't connect with the iMac. The iPhones also used to work through the Sony/iMac setup, but now they also won't show, we are now only limited to music through our computer and not through the Sony Receiver and speakers , oh! what have we done.

Your help would be greatly appreciated, we miss our music, thanks again, Craig