Can't get analogue out from mobo

[tman]

I want to output HD audio over the 3 x mini jacks on my ASUS M2NPV-VM to my amp. I've split each jack output to 2 x phono, and am then feeding the 6 phonos into my amp. O/S is Vista Ultimate, using PowerDVD Ultra to decode HD (Blu-ray) using an ATI 2600XT. I'm basically doing this because it's the only way I can get anything close to uncompressed PCM 5.1 audio from the HD movies at the moment.

For normal TV viewing I'm outputting the video/audio from the 2600XT via HDMI, and this works fine. I know PowerDVD has a 6 channel output option, but I'm getting no audio out when I select this. If I set the Vista audio default to be 'Speakers' and '5.1' I click on each speaker, but get no sound from anything.

I've disabled the 'mic' and 'line-in' options in Vista, so the jacks can be used just for outputting 5.1 audio, and I'm running the ASUS Vista Soundmax audio drivers. This mobo also supports 'jack-sensing' yet Vista doesn't list any info from the jacks in the Sound applet.

Am I missing something. Seems like a lot of people have this working, so I can't believe it's that difficult.