Posted this before as response / solution to a common misconception since X3 (i.e. if you disable this option you may see your CPU meters leveling off a lot lower):
 
  
I have also observed higher readings on Sonar CPU meters, interestingly also when play back is stopped.

I wonder if that has something to do with recent changes to FX tail handling and/or VST3.

Always Stream Audio Through FX. If any tracks or buses contain active plug-in effects, the audio engine will be activated and stream silence through the effects, even if the tracks have no audio data or Input Echo enabled. You will typically only disable this option if you want to conserve a bit of CPU processing if you play a project that contains lots of empty audio tracks with effects. There are several benefits to having this option enabled:
- Any effect with a “tail” (reverb, delay, etc.) will finish playing when playback is stopped.
- Effects will respond to automation envelopes, even on empty audio tracks.
- Many plug-ins do not update their UI properly until they receive audio input.
 
 

Pict
Thanks for the advice Mettelus I tried every setting but still no go maximum 6 Nebula instances as before.The audio interface is a  Cakewalk Sonar V-Studio 100  I don't think there could be a more compatible system  with Sonar than their own interface with their own ASIO driver. I think I'm out of luck trying to use Sonar with Nebula.Thanks again for the help.

That is actually a Roland interface and driver. While our name is on it, the only thing the Boston office really did was code the control surface plug-in. 
 
Edit: Just to clarify. There's no secrete sauce with the Cakewalk or Roland interfaces in regards to how they work in SONAR beyond control surface functionality. 

FreeFlyBertl thanks I just tried your suggestion but it made no difference also I tried using Reaper with an ASIO buffer setting at 128 samples and it still played back smoothly but Sonar playback was total distortion like elephants walking around in a swimming pool filled with packets of crisps(potato chips)miked through a marshall amplifier at full volume.To get Sonar to playback smoothly the buffer settings had to be set at 1024 samples.This is only with Nebula being used and I haven't had this problem with any other plugins in Sonar.

Is this Nebula 3 or Nebula 3 Pro?

Nebula 3 pro server

The thread is getting pretty long. I saw the question asked but not answered on page one regarding the setting of the ThreadSchedulingModel in AUD.ini. The default value is 1. Setting it to 2 may be a better setting for a quad core processor.

Hi scook it is set to 2

Interested in these recent Reaper/Sonar comparisons, I tested the latest Reaper against Sonar X3d.
 
I used Sonar's TL-64 Tube Leveler plugin to test, since it strikes me as a pretty plain vanilla processor without a lot of weird tricks going on.
 
I put 64 instances in Reaper and in Sonar - 8 tracks of audio each with 8 instances.  I turned Reaper's "Anticipative FX processing" off, and Sonar's "Always stream Audio through FX" off (not that that should make any difference), with ThreadSchedulingModel in Sonar set to both 1 and 2.  The computer is a i7 3770 with an RME interface at 1024 samples.
 
I watched the Windows Task Manager as I played back in each program.  In Reaper the CPU usage hovered between 10 and 12 percent, while in Sonar it hovered between 10 and 16 percent, with a spike to 20 percent immediately on playback start.
 
It comes as no surprise to me that Sonar's CPU usage would be higher when performing the same task, because Sonar in general feels like a program with more overhead.  For one small example,the Reaper fx window hearkens back to Windows 98, while Sonar uses more pretty graphics.
 
Sonar is like a Subaru station wagon.  Reaper is a BMW diesel retrofitted to use biofuels.  To worry that a Subaru gets worse gas mileage than the biofuel-BMW is to ignore that the driving experience of the two cars is entirely different.

I'd say... Tesla vs. a Leaf... and the Tesla requires more batteries (cpu) to take ya way farther...
 
my meters don't budge much any more... just avoid buying all the garbage corporate america shoves down our throats... Peets coffee is the hardest...tryin' to do what we're doin'...with a tinker toy is crazy... and as soon as DIVA came out, my once mighty i7 950 rapidly became a tinker toy...
 
but...i digress... as my point is...
 
my meters don't budge much any more...  and that's really nice!  No whining, no forum time, no bad mouthin'... just creatin' with way fewer headaches...
 
just look at everything you bought last year... all the junk/junkfood/$50 movies... and just think how easy and healthier you'd feel if you could say, 
 
"my meters don't budge much any more..."

Isn't BMW generally considered the more luxurious driving experience over Subaru (or most Japanese cars)? :)