EXS 24 Logic Sampler Users Group

What you asked for was possible using some workaround (described in the LUG
FAQ here: http://logicfaq.omega-art.com/) in previous versions as well,  but
Logic had to be in play mode to make it happen.
With Logic 7 layering virtual instruments (or splitting signals to play
multiple instances simultaneously) is just the same as layering external
MIDI sound modules. So you could split by input device, MIDI channel (or
simply select multiple AUs in the arrange) - whatever does the job for you -
and connect the splitted cables/signals to individual EXS instances.

- Sascha