Beginner Question:  This should be simple...Can someone tell me how to set up to:  record an audio track directly from an instrument track within Sonar X3.  I have a Midi track & instrument track (Omnisphere) open, which I can play OK. Now, I want to record the output of the instrument track directly INTO the audio track. I assume that this is possible? Thanks to anyone who can tell me how to do this.

https://www.youtube.com/watch?v=-X-fIfLFtvM , thats how it works in Splat ;P

You can output to an aux track and have that aux track as the input of an audio track. This video will also expand your knowledge:
https://www.youtube.com/watch?v=rCAlFThGvH8
 

Solutions for X3 and older http://forum.cakewalk.com/FindPost/3000845
The new SONAR can directly record synth audio as of Sept 2015 with the Ipswich release. No aux track or patch point required see https://youtu.be/3O9K3BydnCs
 

If I understand your question, what you want to do is "Bounce to Tracks". Please look this up in the manual/guide for a full explanation, but in an nutshell you select the track, then from the "Track" dropdown select "Bounce to Track(s)". You can select "Entire Mix" "Tracks" or "Bus". For starters, select "Tracks" and go from there.
 
Here is an online manual I use fairly often:
https://www.cakewalk.com/Documentation?product=SONAR%20X3&language=3&help=toc.html
 
Bounce to Tracks is in there. Search for it in the index.

For X3, in a word...  Freeze.