Audigy 2, Problems with S/PDIF out

Hi all,

i just got my self the "Creative Audigy 2" card, so i can have sorround sound on my computer. I connected my "Yamaha RX-640RDS" (wich supports DTS, Dolby, Dolby EX and many more standards) with the S/PDIF connector in my Audigy 2, so far so good

When i let set the Yamaha decoder on "Auto choose input" i get sound, but only in Stereo, if i switch to DTS i get no signal at all (not from DTS DVDs (yes the DVD-ROM has a digital connection to the Audigy2), not fom media player, nothing). If i switch to Dolby, i have only stereo again.
If i run the Speaker test from Creative, only left and right speaker respond, others stay quiet, no matter wich format i chose.

So basicly im quite out of ideas what else i could have done wrong (switched from 48 to 96khz, enabled / disabled AC3 decoder, tryd several speaker settings 5.1 and 6.1)

The only thing that confuses me is, when i manualy enable DTS no sound comes, when i manualy enable analog signal, no sound either (sure, its on the digital plug ), but when i set it to auto, the Yamaha puts on DTS, but with PCM enabled.

Okay i guess this should give you a rough overview

Hope someone can help me out @@ im realy lost here.

Alex