The Belkin Switch2 is a range of KVM switches to switch between 2 computers. Some of the range support usb keyboards and mice and include stereo audio switching, it is these particular models which are of interest.
Software isn't required for out of the box functionality but it can be used to enhance it. Belkin have released software for Windows & Mac that allow the audio and video to be switched independently. Belkin haven't released official software for Linux. This is problem for me as I wanted to use the KVM with a Window and Linux machine.
So I did a bit of searching. In other parts of the world the Switch2 range is know as Flip. The hardware is the same just a different name. Some kind person has created a Linux application called 'flapjack' , a command line utility to perform the joint or independent switching functions.
It requires "Device Drivers > HID Devices > /dev/hiddev raw HID device support" to be compiled into the kernel to work (Tested with Gentoo-sources kernel 2.6.22-r2). Just build the package and your ready to go. It's simple and it just works.