Thanks for all the replies.

As I have stated, I tried all types of DVDs, so Regions are not the problem here. Trust me on this.

Actually, almost as soon as I posted my problem (and sent an e-mail to Creative), I found out something great.

I had ASSUMED that VLC Media Player CANNOT play DTS tracks. I was WRONG!

I put in my DTS Demo DVD and played it with VLC Media PLayer. It worked! And the sound, oh the sound. The Gods will dance!

So my problem can be considered solved, since I can now play DTS tracks on my PC, but the inherent problem actually still persists.

Why can Windows Media PLayer decode only Dolby Stereo?
Why can't PowerDVD play any DVD-Videos?
Why can't my Mediasource even detect my DVD-Videos?

Let me try to get some screenshots so you guys can take a look at it.

And thanks for all your replies!