how can I redirect a single instrument in Apple logic to different outputs on my mobilepre? I would like to send all my track instruments to mixer and just the track where I have prepared a click sound to my drummer who will be using ear buds.
The best you can do with the MobilePre is to have two mono channels: click on one and tracks on the other. This is probably not what you want.
I think you're going to want an interface with at least 4 independent outs: one L/R pair for the PA tracks, and one L/R pair for the drummer getting the click. Depending on how loud the PA is and how isolating the ear buds are, you may or may not need to mix a little of the tracks into the drummer's click track to help him/her keep his/her place.
A Fast Track Pro should be able to give you the two independent output pairs; the Fast Track can't.