Why? Can't Logic use the Mac's own multiprocessors, such as the Intel quad core Xeon? Even low-end daw's such as Tracktion can do that. It splits the tracks up for each processor, and makes the work light. Not Logic?
No, Kontakt has it's own Multiprocessor support that should be disabled when using it as an AU in Logic, because the host regulates the threading, not the plugin.
The K3 manual is not so specific:
"MULTIPROCESSOR SUPPORT: If enabled, KONTAKT will
try to make use of
multiple CPUs or dual-core processors, if present. Note that by their very
nature, *low-latency applications are not very well-suited for running on*
*multiple processor cores*; therefore, low system latency values will eradicate
the advantages of multi-core processing."