This article concerns Mac OS X users only
First thing to do is to add Instrument track at set there multi output version of D16 instrument as sound generator.
Then you have to create Auxiliary channel using Mixer's options.
Set it up as Stereo channel, but don't bother with Inputs or Outputs at this stage.
Now in Aux' I/O section set Input to feed the Aux channel with signal from altenative plug-in's out. Stereo pair 3-4 corresponds to output 2, 5-6 to the plug-in's out 3 and so on.
Don't forget to set up the plug-in to send signal to different out.