I will probably add a 3rd later on which will be the last - primarily because my Dr Bott KVM only supports 4 devices.
I've been using Windows Remote Access; my KVM has been sitting unused on the floor. There's now a Mac client at www.Mactopia.com, and it works spectacularly well. Of course it's not as fast as a direct connection, but it's fine for slave machines, and I like having the Windows machines in windows on the Mac.