There are also some special made products that will dock your ipad into an interface (Alesis for example). I'm not too sure how well they work within Logic however. And there are some midi docking stations that will use the synths on you iDevice and let you play real keys. Again, not sure how effective they work as I have yet to try them.
Ok thanks. I've tried the headphone jack to 1/4" jack but the interface signal light on either input is weak to nothing at all and the sound is incredibly distorted. However I don't have another instrument to connect and see if it's not the interface :-s. it is new though.