It could be the HP or it could be the Sammy. Do any other sources give you 5.1?
I have a HP laptop with HDMI output. I also have a Samsung HT-C6600 5.1 home theater system. I have the laptop connected to the HDMI input on the receiver. I am able to get audio through two of the speakers only. The video works fine. Any idea how to get the 5.1 to work with this setup? I ran a 5.1 audio test from the laptop and it still only came out of the two speakers so I know its not a media file issue.