As far as mobo go I really don't trust anything that isn't made by ASUS or Intel. Maybe it's just me but it seems like a disproportionate amount of people with mobo other than those complain of problems.
Before wasting a lot of money on a new machine I'd check into spending a couple of hundred on a new motherboard. Also, check those DAW making companies like Carillion. All I did was copy their system as I assume that they did the research.
Also, realize that your system may not be tested with music software which is a good 6 months behind the technology trend. Dual Opeterons are pretty well tested tried and true. Again check to see what the DAW manufactures are putting together then try to get your system as close to that as possible.
Edit: One more thing. Hold on to your dual AMD 64's. Wide spread support for dual, dual core is just around the corner.