I use JABB with Kontakt2. Generally, I use Kontakt2 in DFD-mode. In the saxophones there are groups called "legato (no DFD <= loop crossfade)". For these groups I choose "sampler" in the source module, leaving the other groups on DFD.
In the brass instruments there are too legato groups, but without the hint "(no DFD <= loop crossfade)". Should I adjust these groups to "sampler", too?
I recommend using everything in RAM except, perhaps, piano and cymbals - and even those if your computer can handle it. Like GPO, JABB is designed to run best in RAM. But it doesn't hurt to experiment to see which combination works most successfully with your particular hardware/software.