Digital -> analog sound for wireless headphones

Please help with a wireless headphone setup.
My system is BD player --> Yamaha RX-A720 receiver --> TV, with both connections through HDMI. I just got a pair of Sennheiser RS-120 wireless headphones, and connected it to the RCA  sockets labeled "Audio Out" on the back of the receiver. When I listen to internet radio or AirPlay the system works well. 
I want to be able to watch movies with the sound delivered through the headphones.  Yamaha support suggests using the 1/4" front phones jack, but sometimes I need to have the speakers working at the same time. 
Is it possible to have the system output the sound from the BD player somewhere on the back panel? Do I need a DAC? 
Many thanks.