In most cases ( If there's a unknown keyboard attached ) , you can choose for: "keyboard w/o controllers" in the "add device list" ... , so you can play almost any kind of keyboard with midi-out ... (midi in aint important , cos Reason doesnt send back anything ... besides sound .. lol)

And if you're IMac has a midi-in , then its just a piece of cake 2 do ... (am on a XP machine , here its just a matter of plug in , choose keyboard w/o controller , and go ...) , otherwise you have to buy a midi to usb adapter ...

Hope this will do the job for you ...

Greetzzzzzz