Mono differs from stereo image

Try making a copy of your project, then making mixing adjustments and decisions in mono and see how your stereo image differs after those decisions.
By the way, is there a specific reason why you have a stereo snare track?
 
Mono Compatibility Pro Tip

 
 
This is so hard to explain.
I am sorry if this is not making sense.
 
All vocal Pan pots are centered.
I am doing this in Solo.
Whether I use the Sonar stereo interleave or Mono-interleave on track or bus, it is placing the image (my lead vocal) in the same place.
When I play a stereo song from the internet through the Aux on my My Presonus Monitor station, it places the image in what I would call the center.
But using the PreSonus SOURCE return, when I listen to my tune in Sonar the center (the same lead vocal) is off to the side.
 
If the internet through my Presonus Aux is correctly centered, then I have done something to trick Sonar into placing the image off-center, even though there is no panning.
 
Any ideas?
I'm missing something.
 
Thanks in advance,
Ray

Thank you for your suggestions.
 
I wouldn't know where to start with the screen shots.
 
I'm convinced that this is an operator error (errm - ME!!!LOL!).
 
Thanks again,
Ray

Thanks J,
I'll check that (snare and ctrl+O) out.