vorbis sound sudders with ATI HDMI 7.1 audio (4700 series)

I'm using a Radeon 4700 card and am using the built in HDMI audio. When I am using a Vorbis decoder and Zoomplayer, the problem is that it is not clean, processing MP3, sound is find so is AC3 and DTS sound, but if I send a multichannel Vorbis (normally 2.0 or 5.1) to the Receiver it is not clean (everything kind of shudders). I've tested with all the possible supported directshow filters in ZP 6.0 and everyone of them shows the same issue. I've also played with the Vista Audio options and tried reducing the number of speakers (7.1, 5.1 and even 2.0) and also the max/min output levels (to 44.4 and 48, normally I allow up to 192). No matter what I do it shudders, if I switch to the realtek onboard it works fine, but then I have jitter issues and I want to use the HDMI audio as it reduces the number of cables I must run.


I'm at a loss at this point as to what to do to resolve the issue (other than encode the Vorbis streams into AC3, using ffdshow, but this does not seem like a solution only a work around.


My receiver is a Yamha 1800R.


Any idea what I can do?

ERIC