I have an Onkyo tx-sr605 receiver and a Sony bdp-s550 Blu-Ray DVD player. They are connected via HDMI. When I play back a DVD, the Onkyo displays TrueHD. My speaker setup is 5.1. However there is no sound from the two rear speakers. If I switch over to Satelite (or any other source), I get 5.1 sound. Any suggestions? Thanks in advnace.