Audigy 2 Platinum soundcard with a Logith Z-680 speakerset

Hello,

What is the best way to connect an Audigy 2 Platinum soundcard with a Logith
Z-680 speakerset.

I have connect it with the three audiocable as in the manual and also with a
digital coax connection,
but when I want to test the speakers with the software of Creative, I hear
only two speakers, not
all. When I play a mp3 or a DVD, I hear all the speakers (sometimes not the
center speaker).

Am I doing something wrong?

Can anybody help me?

Thanks in advance,

Jos.