One through RGB, the other through composite... not ideal, but instant and it works (provided that model has the socket(s) on the monitor).
Ed: I've used A500+ through RGB with A1200 through composite on a 1084S, because that way they were both in colour, but usually I used (a few years ago) to have the A1200 on RGB and a VCR as a tuner feeding through the composite so I had RGB monitor with TV at the press of a switch.
