Sometimes responses are so cretinous that they really don't diginify a response. It's easier to think everthing's sh.it than try to understand.
Ah well, I'm obviously a masochist...
I'm guessing here, but you can't select your USB mic device on it's own under Logic because it is not actually a full audio interfaces - it doesn't have inputs
and outputs, it probably only declares one input to OSX. Logic is looking for a device that at least has some outputs otherwise it think it's pointless selecting it as it can't be used to hear anything anyway.
So it's actually a
feature - it it didn't do this and let the user select
anything, we'd probably get a string of forum posts going "I've selected my USB mic in Logic and now I can't hear anything!".
So, the
correct procedure, as mentioned
numerous times in this thread alone, is to
add in the extra mic inputs into your regular audio interface - this lets Logic output to your speakers/phones/amp whatever, so you can still hear the output of Logic, but will
also let you record for the extra new input from your mic.
In order to do this, is to add you regular device and your mic device into an aggreate device. This aggregate device has inputs and outputs and so can be selected in Logic, and everythings hunky dory.
If you find this complicated, don't understand it or see why this is the case, perhaps you
would indeed be better of with Garageband.
shrugs