AMD Processors users, what about Sonar X2a and X3 stability?

AMD works just fine with X3, as it should. There really isn't much to say about the issue, there's no reason to think that AMD might be less than compatible because, heck, x64 processing is an AMD design, not Intel's.
 
 

I built a new DAW late last year using an AMD FX-8350 8-core processor and have had absolutely no issues because of that. I've actually had more problems with the Nvidia drivers (introducing latency) for my Geforce card than anything else.