The source determines what audio format is sent, not the receiver. If the source sends DD, then the AVR will decode it, turning it back into PCM. The same goes for DTS sources. If the input is already PCM, then there's no decoding for the receiver to do.
How is your DirectTV box connected to the TV? Device audio connections should be go directly to the receiver, not through the television. TV's are two channel devices and will only output stereo PCM in many circumstances.
By way of background, PCM is the basic language of home entertainment audio. Movies and CDs are mastered as PCM and receivers are designed to process PCM. 5.1 movie soundtracks are very large and studios use data compression codecs such as DD 5.1 to save space on discs, much the same as zipping up a data file. The large PCM track is fed into an encoder, which compresses it. The decoder decompresses it back into PCM. So, you will always ends up with PCM, even when the the source sends DD or DTS. Also, PCM is not output to the speakers. Rather, it gets sent through a digital-analog converter (DAC) to produce an output that can drive a speaker. So, when your AVR display reports LPCM, that's the format of the audio input, not the output.
Edited by BIslander - 4/24/13 at 7:27am