Thus far, I've only tested the digital out of HBO and Star Movies from the coax of the STB going into the receiver.
For the films I've seen in HBO HD, the implementation of the 5.1 digital out is wrong. You get the voice from all of the channels, including the surrounds. No panning of sound whatsoever. It seems the center channel is merely replicated in all the other channels. Selecting two-channel PCM digital out for dolby prologic or dts neo processing, only the center channel gets active.
For Star Movies HD, actual surround information is decoded by prologic and dts neo using two-channel pcm, leading to the conclusion that the star movies hd pcm out is indeed two separate channels unlike the hbo hd pcm which, I suspect, is only really one channel.
I don't know if the above will also hold true from the hdmi out going into the receiver since my pioneer receiver does not have hdmi