Help with low HDMI 5.1playback in latest XBMC nightly build

Hi

A couple of days ago I upgraded to the latest XBMC nightly build which features the new Audio Engine.

Now I realize that these builds are not stable and contain bugs especially the Audio Engine as it had been rewritten from the ground up.

But here's the problem.

When I set the number of channels in XBMC to anything other than 2.0, (e.g 2.1, 3.0, 5.1, 7.1, etc) movies that carry digital audio (DTS, Dolby Digital, etc) will play will play very slowly for almost a minute and then it will play at the normal rate for about 10 seconds before it completly freezes. Thi s is very reproducible.

My Setup
Ubuntu 11.10
Radeon HD 5670, 12.6 drivers,. VAAPI enabled and working.
2Gig RAM
2.0Ghz duel core CPU
HDMI cable from media PC to TV

I use HDMI directly from the media PC to the TV as I don't have a receiver yet. You might be wondering why I was using anything other than 2 channels. Well I was just playing around with some extra speakers that I have and happened to notice that it has issues if setting it to anything other than 2 channels, but I am looking at getting a receiver soon anyway.

I tried setting XBMC to play through HDMI and Analog, but both give the same result. I tried all of the different output and passthrough devices available
I also tried with VAAPI disabled.

I've turned off all of the audio decoding options, DTS, Dolby, AC3, TrueHD, etc, I've even tried with them all on.

So far the issue remains.......

Has anyone else had this problem and/or know how to fix it?

I don't know how to produce debug logs, so if you need them just tell me how and i'll post them up.

Thanks