no surround sound on dvd

I rented a classic comedy, National Lampoon's Vacation 20th anniversary edition (1983 original).

I cannot get surround sound at all, at least I'd like to get stereo 2x like I do on my mp3's and
general video clips (online like Godtube or local). I have a Logitech 5500 5.1 surround system
and set the settings to Coax Stereo x2 (2 speakers duplicated to rear). It works with
everything but this dvd, and there is no audio options on the dvd menu for the movie.

I tried another movie, released last year and it worked fine on x2 stereo mode.

One thing I noticed, with Vacation I only get sound coming out of the center speaker. Strange. Also, the LED display on my Logitech receive says "digital", whereas usually it should say Coax Stereo x2. It was on that setting until the movie started playing, it switched itself to digital only and center speaker only.

I'm watching via Media Center dvd, through an hdmi connected to my 1080p TV.

Probably irrelevant, I have a Creative Soundblaster Live 24bit external sound card with official 64bit drivers from Creative (latest drivers).

Specs
Vista 64bit Ultimate SP1
DVD watch via Media Center / HDMI cable to TV
Logitech 5500 5.1 Speaker System / Coax Stereo x2 Settings
Media Center: 5.1 audio settings

 

Hi folks, hope someone can help me out on this. Thanks.