There is no reason to use bounce. Freeze does exactly the same as bounce except you can unfreeze. Freeze should be done from the synth rack. It makes it simple.
 
The way I do it is. Set up the audio track/s you need then set the output of the synth to the audio track/s you made. When you freeze the synth those audio tracks will receive audio from the synth. No need to move or bounce anything. 

IIRC Sonar has been able to record the synth audio output to it's track for a while now. just click the synth audio track record button and then rewind and record.
 

Multiple ways to accomplish the same general idea here. Bounce to Tracks works when both the MIDI source and the audio output/synth track are both selected. Freezing will render the current synth output and disable the synth so it's not running in the rack. About 2 years ago we implemented the recording of synth outputs as well as a feature request.
 
Ultimately, the best approach depends on what your needs are. Bouncing to tracks will create new audio tracks, you would just then need to mute the original synth tracks unless you want both the synth and the audio tracks playing in real time.

I just freeze the synth, not the track(s)
 
This will freeze all audio tracks connected to that synth in one pass.

I appreciate all the help.  I just thought I had recalled a way to bounce/freeze a dozen or so tracks at a time some easy way.  I must have been mistaken.
 
Speed-wise, it just seems to be as productive to bounce/freeze them one at a time.

You can freeze multiple channels of a synth in 1 click if you've set up multiple synth audio outs of say Kontakt for example, with multi synth audio tracks each pointing to various audio outs of that synth. I used to freeze synths, until the occasional un-freeze would result in the original synth patch not properly reloading, at which point I switched to bouncing to track. After bouncing to track, I simply disconnect the synth in the synth rack. It's easily reconnected and loads all synth info more reliably than freeze. Also good if I've edited timing or volumes or crossfades of the synth audio and need to just re-bounce a specific part. Also I moght bounce different Mic positions of the same track to choose or blend. Or instead of setting up multiple synth audio outs for drums, just solo the kick in kontakt mixer, bounce to track, solo snare, bounce to track, solo hats...etc. Also, In platinum or Cake i miss the take lanes once a track i frozen. Not a problem in X1. 😉 of couse in X1 miss side-chaining.