Hi Jason -
After you load the Sitar patch, go over to the Channel Strips panel at the right (hit Cmd-6 if it's not already showing), and open the EXS24 Virtual Instrument plug-in. There you can tweak the tone (Filter) and envelope (ADSR Env 1&2), along with other adjustments to the instrument sound & playing response. If you want to dig into EXS a bit, I've linked to an EXS course that covers both the basics and more advanced features for customizing an EXS sound & playability.
Btw, I've moved this thread to the MainStage Sub-Forum