No Surround Streaming with Samsung Blu Ray

I just set up my Samsung Blu Ray player to stream Blockuster movies. I had originally set up my TV but that did not work too well.
The Blu Ray streams the movie fine but I only get sound from the L,R and Center speakers. No surround. When I play a movie on disc the surround works fine. I have a Denon AVR 2112 receiver and a new Samsung Blu Ray. I've tried all the different settings in the Samsung Blu Ray menu to no avail. The current settings are PCM, and also set to surround mode.
I've never streamed before, so am wondering do streamed movies not play in 5.1 surround? I did get a movie from Comcast's pay per view and it played in Surround so I'm a little confused.
Movies aren't as much fun with just 3 speakers.

I talked to the place I bought my TV and Blu Ray from and they said Blockbuster does not stream in 5.1.
Could this be the answer?

Mark,
You may be right about the center speaker. I just did a quick listen and probably assumed it was on. I'll double check it today.
The person I talked to at Magnolia Hi Fi (My retailer) told mr to use VUDU. I remembered there was an app already loaded for it on my Samsung. They have boldly displayed 5.1 and digital quality movies. Just watching the trailers I could see a big difference in picture quality compared to Blockbuster and Comcast. I still did not get surround watching a few trailers at VUDU but I have to assume the trailers are not broadcast in 5.1.
I noticed the VUDU movies were $2.00 more to rent as opposed to the others but I'd pay it to watch a movie with a good quality picture and 5.1. That's why I spent all this money on my setup.
I will call Blockbuster and report back.