What audio formats do Direct TV use?

HD is Dolby Digital 5.1

Is it even possible for cable to show TrueHD/DTS-HD?

Is it even possible for cable to show TrueHD/DTS-HD?

These are not audio broadcast formats.

Is it even possible for cable to show TrueHD/DTS-HD?

It is technically possible that a broadcaster could decide to broadcast them and issue set top boxes with the right licenses to decode to PCM for non-HDMI 1.3 output (as the PS3 does), or bitstream via HDMI 1.3.

HOWEVER - I don't think any broadcaster plans to do this and I know of no set top box that supports it.

Additionally, HDCam (which only has 4 PCM audio tracks which isn't enough for the 8 required for stereo + 5.1 mixes) has to use systems like Dolby E lossy compresssion - which is compressed - so there would be little point in using a lossless formats for broadcast (and you'd be better off putting the wasted bandwith into the video stream?) HDCam SR can support 12 channels of PCM audio - so it would be feasible to TX in TrueHD or Master Audio - but I don't see it happening for regular broadcasts for a while... (Again VOD may be different)

Is it even possible for cable to show TrueHD/DTS-HD?
It no more likely to happen than seeing SSDS on home video formats.

Sound formats have specific purposes and are used where appropriate.
HD is Dolby Digital 5.1
No, HD is simply Dolby Digital. The number of channels can vary depending on the program. It is very often 2.0 or 5.1. Hoowever, it can have other numbers of channels, especially in the case of older films remastered for HD, but containing the original audio channel arrangement.

Good. Next time my STB DVR HDMI connection craps out, I'm going component/optical.