polarbear

stevec
FWIW you can use a SIT and multiple outputs.   I do that for AD2 quite often where I'll start with a SIT, and if the project seems to need it I set some of AD2's individual kit pieces to separate outs than add audio tracks whose inputs are those AD2 outs.  From that point I typically keep the stereo elements (cymbals, OH, Room) on the main SIT.  
 
I've done the same thing for KONTAKT too, though I usually have to remind myself how to add outputs after the fact since it's not quite as straightforward as AD2...    Unlike many others I actually do prefer to use SITs when I can; they've become a standard element for me.    Fortunately I haven't had any real issues, knock on wood. 
 

Hmmm... OK I'm gonna have to try this later... Here's my thinking:
 
Omnisphere Simple Instrument Track
Load Piano in Channel 1, Bass in Channel 2, Guitar in Channel 3
Create 3 MIDI Tracks outputting to Omnisphere and have the channel of each be Channel 1, 2 and 3 respectively.
Make my Music.
"Oh but I want to add Guitar Rig on the guitar sound on Channel 3 without it being on all 3 sounds."
Add an Audio track, Add Guitar Rig to the FX Bin of that Audio Track, Set Omnisphere Channel 3 as the Input of that Audio Track.
=
Still managed to use only one instance of Omnisphere reducing my CPU usage while still being able to add effects to only a specific instrument.
 
I don't have it up in front of me right now, so I'm not 100% that is all doable and would work, but I THINK from what you just said, that should be doable, right?

Yes, what you're describing is what I do with AD2 and occasionally Kontakt.   That is, "a single SIT is all I need for this!", followed later by "you know I could really use something on this one channel"...       I don't have Omnisphere but it sure sounds like it would operate the same. 
 

stevec
FWIW you can use a SIT and multiple outputs.   I do that for AD2 quite often where I'll start with a SIT, and if the project seems to need it I set some of AD2's individual kit pieces to separate outs than add audio tracks whose inputs are those AD2 outs.  From that point I typically keep the stereo elements (cymbals, OH, Room) on the main SIT.  
 

 
Just wanted to say THANK YOU stevec. You did it. It worked exactly how I wrote it out after reading your reply. Super easy, and means I can still use Instrument tracks for everything... Until I need a 2nd out from Omni or Kontakt (or Addictive Drummer 2 actually, I never thought about doing that... that's a great idea), and then I can just add it, change the channel, make a midi track, make an audio track with the in being that channel of whatever I'm using and then boom, I can add separate effects.
 
Killer.
 
Thank you.
 

Hey...  you're welcome!  
 
I know that many would never use SITs over the traditional split track design, but I really do prefer them.  I usually don't know where I'll need multi-outs at the start, and having finished many projects using nothing but stereo outs I don't those projects have suffered for it.