OK so for me, there's been a change. I'm no longer getting any white noise through the amp when playing any HD audio stuff. The only problem is, I'm getting no noise at all now. Again forcing it to the lossy codecs works fine. DTS & DD work no problem at all, so thanks for that.
I'm not sure whether you're going to continue looking into this, but I appreciate the effort you've already made and thank you for all the existing work to get it to where it is!