EXS 24 Logic Sampler Users Group

from len ( Logicaudio mailing List) :
You can do this with hardware synths or one virtual instrument and 
one hardware instrument, but you can't do it with two virtual 
instruments, because the Environment will only communicate with one 
at a time.

Use a transformer assigned to an arrange track. Cable the top outlet 
to the instrument serving one of the destination synths and cable the 
next outlet to the instrument serving the other. (One of these can be 
an audio object for a soft synth.) Set the transformer mode to 
"Condition Splitter ...". Set the condition status (top row) to = and 
"Note". Set the Pitch condition <= and set the note number to the top 
note of the bottom half of the split.

Len