For starters your in the wrong forum, this is for Sonar 8.5 and earlier versions.
X1 is a little different so it might be a good idea to post there instead.
I agree that you must be overlooking something basic as this is a very simple process that I myself have done many times with guitar tracks for the same reason you wish.
( in 8.5) Highlight the 2 tracks.
Dropdown Menu- bounce to tracks and choose the source and destination and stereo.
Note:
In your screen shot it appears you have failed to highlight or choose the 2 tracks as it shows entire mix as source.