Excessive cpu usage even when idle.

Pertinent specs:

Toshiba Qosmio X505, Intel i7 cpu @ 1.73ghz, 6gb ram
Sonar 8.5.3
Windows 7 64 bit home edition
RME Babyface interface, latest drivers and firmware.
Sound libraries are on an external dedicated eSATA drive.

The issue is soft synth performance, or lack thereof.  I've tested with 2 so far (Dimention Pro and Omnisphere), in a new and empty project.  Doing nothing at all, I'm seeing about 20% or more cpu usage in Sonar.

Here's my audio settings, if they help:






Here's what the cpu meter in Sonar looks like during a typical Omnisphere patch playback:



And task manager during the same time roughly:



The thing I find concerning of course is that I see far less cpu usage in Reaper under the same circumstances (even there, going down to 48 samples (the lowest the RME interface will allow), I'm not seeing cpu even come close to 10% usage, and idle is obviously far lower.



Any help would be really appreciated, let me know what other info you might need from me to try and resolve this :)

I should also note that WDM mode just makes this provlem worse.

Looking at the multi core Sonar CPU meter in your screen shot one virtual core is running at over 50% and the others hardly at all.
 
This indicates to me that the CPU meter on the task bar is showing the utilization of the busiest core. In reality you are using around 6.5% or your available CPU capacity.
Some VSTs have setting that multi core support turn on and off check the Omnisphere manual.
As for Dimension Pro I have had at least 12 instances of Dim Pro with half a dozen other VSTi in a track + a number of effects and still have plenty of headroom on my i7.