I feel ya, it can be very frustrating. I haven't really read through your whole thread, but I also have a new 12-core Mac Pro, no pops or audio issues and no video problems with a Radeon 5870; thing is, I'm using dual 24" Apple Cinema Displays on MDP, which seem to have no particular issues.
New hardware often exhibits driver problems and occasional hardware issues, Apple does their best to address the problems, often not until a fire is lit under their *** and many people complain and some of the larger sites write some copy about the problems, but overall their gear has to work, or nobody would buy it.
If you read through the forums here, you'll obviously see this whole huge tidal wave of anguish and anger about a variety of issues. That tends to be because people experiencing problems eventually find their way onto the forums here, whereas those who aren't having any problems, just go about their lives, using their gear.
If I were you, I'd be pretty unhappy too. You really only have two options, as I believe somebody previous mentioned.
1- Return the Mac Pro. I think you have something like 2 weeks to return it with no questions asked, you can say you don't like the way it looks, and they'll take it back. You're obviously experiencing significant issues, and it's doubtful you'd have any trouble getting your cash back and then buying a PC or whatever you want.
2- Just accept that it's new hardware, new drivers, and that no matter how many new units they send you, it's not going to start magically working with the display you want to use, until the drivers are updated. If you can live with it, Lloyd offers a workaround for the issue here:
http://macperformanceguide.com/blog/2010/20100910_HotCorners--macpro.html
I'm not sure anybody with a dual-hex has experienced the audio popping issue, thus far that one seems to be relegated to the single CPU 3.33GHz boxes.
Sorry your experience has been so crappy so far, you obviously have your reasons for wanting to own a Mac Pro, so you should consider what they are, what you can live with, and if you can't accept the current situation you are dealing with, just return the Mac and buy something else.