Right, looking again at the wiring diagram for my amp it shows that the front preouts are on the far left - but these are the ones I have removed as they were driving the rear speakers!

So it looks like when my amp was installed the wiring was done incorrectly. So if I move the connections from the right hand connectors to the left ones, I should be good to go I think.

If you can excuse my poor MS Paint skills, the attachment shows roughly how it's all wired up.