Hi Phil, you are correct, there is no + button in the Mixer - sorry - I forgot that feature is not in Logic 7...
I don't know the interface of JABB. Would it be possible for you to post a screenshot of the interface?
Are the Aux channels you mention in the JABB plug-in or in Logic?
If I understand you, set trumpet 1 to aux 1 and the other channels to the other Aux's.
In Logic, create an Aux... I can't believe I'm forgetting Logic 7 already (!!!) - but I believe yu can do this in the Environment easily or reassign a track header in the Arrange window by click holding on the name and selecting an aux track that way...
Sorry if I'm being vague. I'm finding it hard to recall some of the Logic 7 work methods which have been simplified in Logic 8.