Instead of an i7 950, consider a dual Xeon 5520 box. This is basically the cheapest way to get 2 Core i7 CPUs for 8 physical and 16 logical cores. Plus, you can but hordes of RAM in it so you can run 20 streams in real-time without worrying about memory usage! A 64 bit OS is obviously mandatory, in any case
You can get a box like this for under 2 grand...
~MiSfit