I might not be understanding correctly, but all 8 crossbars and all 10 hotbars can be set to be either shared between all of your classes, or change when you swap classes.

So, if you check all 8 in character configuration you'll only have 8 crossbars between all of your classes (which sounds like your problem).

However, if you uncheck all 8 then you have the full range of crossbars available for each class (20 classes) and each job (10 jobs), giving you 30*8 = 240 distinct crossbars divided into sets of 8.

In reality you'll probably want to share one or two, but it seems like it should be enough.