IMac digital out help


I recently purchased an imac to feed my audio aero capitole and use it as the DAC. In order to get the digital out i was planning on going toslink and got a mini toslink adapter thinking that the headphone jack is hybrid. To my surprise the mini toslink is quite smaller that the headphone jack. Is my output not hybrid? Do i have the wrong adapter? Should I pursue a usb or firewire digital out instead? Any help would be great.
quaded
It is hybrid. Not sure what adapter you got. I use this and it works fine.

http://www.amazon.com/Cables-Go-Velocity-Right-Adapter/dp/B0002J2MTQ/ref=sr_1_2?ie=UTF8&s=electronics&qid=1282415186&sr=8-2
This is the adapter i used. Still confused...

http://cgi.ebay.com/New-Monster-2-5-Mini-to-Optical-Optic-Toslink-Adapter_W0QQitemZ220644555313QQcategoryZ32838QQcmdZViewItemQQ_trksidZp4340.m263QQ_trkparmsZalgo%3DSIC%26its%3DI%252BC%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%252BDDSIC%26otn%3D13%26pmod%3D370418866102%26ps%3D63%26clkid%3D6241498573553112923
the imac is brand new. The plug is way too small. Apparently it is 2.5mm which is smaller that the standard 1/8" headphone plug. I don't know what this plug will fit but not my MAC. Weird.