edit: I've had a VERY brief look, the Steam streaming doesn't appear to be encrypted in any way, it's just an h264 stream with some additional i/o commands: some resourceful person could probably reverse engineer the packets without too much difficulty. Fortunately, it looks like someone already did: doing some additional googling, there's
limelight which implements the Steam streaming protocol entirely open source. It should hypothetically be possible to port it to the Pyra.