Sorry, I was away. Here is what to do: Run Setup on the 10a and make sure under Easy Setup you have Multichannel selected. You will then see your speaker setup where you can pick speaker size and make sure sub is On. Then under Audio and then Digital Audio Output set PCM DownConversion to Off, Set Dolby Digital to bitstream, set Dolby Digital Plus\\Dolby TrueHD to PCM, set DTS to bitstream, and set DTS-HD to PCM. You will then let your receiver decode the Dolby Digital and DTS via digital coax and the 10a will decode the DD+, Dolby TrueHD, and DTS-HD and it will be ouput via the analog outs of the 10a to the analog ins of your receiver. You could also let the 10a decode everything by setting everything to PCM but I know my Denon receiver does a better job with DD & DTS than the 10a does.
Your receiver does have analog ins, correct?
Update: I JUST NOTICED YOU SAID YOUR AVP HAS NO ANALOG INS. Like the previous poster said certain Fox titles have no DD track, it just then plays back the DTS core. You will need to set everything to bitstream on the 10a. I think that is why the Fox titles are causing havoc because if your receiver doesn't decode the DTS bitstream and you have no analog ins its going to 2-channel. I think its time for a new receiver.