Why make life harder than it is? Used desktops are cheep today and Mach will run fine with an old desktop /2GB RAM. I bought recently a used Dell Optiplex760 for $120 including LCD monitor, keyboard and mouse and Mach is very happy. Dual processors will not make Mach happier but it may help your CAD program IF you make elaborate objects
I will stick with Intel processors and the only components you need are the parallel port, a DVD to install the OS and a USB to copy files. My desktop is a dedicated PC just for my cnc and is not connected to the Internet; the only software installed is Mach3 and I have disabled the sound, modem and network cards.