Anyone have any experience working with the above interface? I could not get Sonar - Artist recognized the signal coming from the XR18. Any hence and tips? 

Hi, and welcome to this forum. I do not have a XR18, but found these two articles when Googling.
http://forum.music-group.com/showthread.php?8102-USB-control-and-windows-driver-options-on-XR18
https://www.facebook.com/BEHRINGER/posts/10153205653278914
Do you have the latest drivers and firmware for your XR18?
All the best.

Are the inputs and outputs checked in your preferences? That's where I'd look first. Does your operating system recognize the behringer? If so, then they should be listed under Sonar's preferences as being available for use.

Go Into Edit> Preferences and have Sonar assign the XR18 drivers. It's a pretty cool interface and works well with my version for Sonar X3 PE. My XR18 was recognized in WIn 10 instantly. If you have other direct XR18 questions check the Music Group Forum. They are really helpful as well.
 
I recall one guy having a problem with the XR18 and another daw, and he was instructed to use a different USB port on the computer. That worked.

You need to treat the XR18 as you would any other USB recording interface. You need to open the XR18 interface software first and make all your input adjustments there first. I'm assuming that SONAR has recognized the XR18. If not, you will need to go to the Behringer site and download the drivers and install them on your computer.