Just when the computer is idle, and when I play audio from SHS6XL it sounds all crackly and distorted.  HELP!!!
 

I figured it out.  Got to use MME driver.  I guess I can use the ASIO.
 

Download the device drivers from the manufacturer's website.  Use whichever mode they recommend (definitely not MME).  If you have any further problems, remember to provide details about your settings and configuration.
 

How to set up the 1818VSL:
http://www.presonus.com/community/Learn/The-Truth-About-Digital-Audio-Latency
 

I've downloaded the ASIO driver from Presonus.com.  When I try to record, I get error message: Audio configuration not compatible.  I've tried WDM/KS driver and MME also.  I had it working before.  I don't know what I did.  Do I need to install the 64 bit version of SHS6XL?   I'm currently running the 32bit version.

Sounds like you have switched clock rates. Look and see if the clock rate matches the original format you were using ( 44.1 or 48. ) 
 
If your computer is windows 8- 64 bit then you should install the 64 bit version of both Sonar and your interface and take advantage of the better performance. You need to match the drivers for the interface with which OS you are using for sure. But you can run either , or both 32 or 64 bit DAW Software on a 64 bit OS.