Very few jobs you run on a home computer can spin up 12-24 threads. Honestly it's rare to stress that many cores in typical business server use, which is why we turn to virtualization to get good hardware utilization.
You should have said that originally. Video is one of the "Very few" jobs that can use a lot of threads.
How much money are you going to be paying for the Opteron and motherboards? The 6176 is two generations old and it's got a fairly slow 2.3Ghz clock speed. You may be better served with two newer Opteron 4300 series (essentially a multiprocessor Vishera)