Update:
I've managed to pick up an ex-install Cloud mixer on eBay - should be delivered early next week, hopefully. I'm not sure of the exact model, but I can see from the photos it has the M2 output module in, which has the auto voice over section. Point taken re age etc; not being an engineer I'm not going to be mucking about with any innards - I'm happy to lose a tenner or so on postage to have a look at one and see if I think it'll do the job. If it doesn't look and sound okay then it's going straight back - I love the Distance Selling regs!
Thank you again for your advice, yo