how to get 7.1 sound from a 5.1 movie...

[HeManster03]

at work we currently have an onkyo txsr606 reciever and panasonic dmpbd55k blu ray player. we get dolby trueHD and dts-master audio HD to show on the reciever and play just fine. we just today hooked up an extra 2 speakers to test out the 7.1 sound, and during A Nightmare Before Xmas(dolby truHD 7.1) we got sound out of all 7 channels and the sound was great. popped in Ironman( dolby truHd 5.1) and are only getting sound from the center,sub, front left/right and surround left/right..absolutely no sound from the surround back left/right. is there a certain setting in each unit that i have to use so that i get my dolby tru HD, or at least have all of my speakers working? any advice would be helpful. i am at work tonight until 9pm, and back at 9am tomorrow, so if i get an answer tonight, ill be very pleased, but tomorrow works also. thanks guys...your all awesome, and always give me great advice.