Queen Greatest Videos 1 & 2 on DVD

When I bought these two DVD my setup for my computer was a 5.1 Soundblaster Live Card and 5.1 speakers. When playing these two I didn't get full 5.1 sound when slecting it in the audio options it was only 4.1.

Since upgrading my sound card to the Soundblaster Audigy 2 ZS Platinum Pro with 7.1 speakers the T7700 I have now got Queen DVD's in full 5.1 when selected in the audio options.

I was just wondering what would have made the difference to it.

The discs are mostly in 4.1.

Using the Audigy2 you get them in 5.1 because the card has a software engine that 'upmix' non-5.1 sources to 5.1 or even 7.1 landscapes.