Hi Tim,
dual head graphics cards (respectively their drivers) usually offer the option to clone the output of one display to another. If I got you right, this might be what you're looking for ... Apart from this, I don't know much about the state of the multiple window branch, nor do I know if it is possible to have two instances of gem render to different screens. However, the multiple window thingie seems to be the better solution to me.
hope this helps, thoralf.
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