Hi
I've got the same soundcard with Powerdvd and it passes DD and DTS no prob = what do you mean by choppy ?? is the picture stable, are you getting stuttering in the picture as well ?? Assume you're paassing spdif via coax... Is there a poor connection in the chain ?? Have you checked the adaptor you're using, (tried another ? - they're pennies in Maplins), check also the cable you're using - try to source a reasonably decent, not too long cable, (i.e. not half a very long audio interconnect - tho' I got it working fine with one of those initially......

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Come back and tell us more.........
Sean G.