I use 5 PC's too for the same reason as Fursphere, if there's no software involved then I know I'm 100% safe from bans. Having said that, I would be happy using Keyclone but less so using AHK due to the scripting abilities AHK has available to it. As I had the PC's available to me when I started boxing then the hardware route suited me better.

To answer the main question in full, I use Multiplicity to create a virtual desktop and a wireless keyboard to control my characters.