I was working on a patch and I needed an 8 voice detuned saw + square sound with a medium-slow attack. My detune was around 3.5 so the patch was relatively wide, approximating a violin sound. I tried bouncing it to mono a few times and instead of getting the nice amplitude envelope I was hearing when I programmed the sound, I got something that sounded like the resonance was turned up on a filter envelope, I didn't have a filter envelope on the patch. When I tried bouncing it to stereo it sounded great. After scratching my head for a while, it turned out that combining the left and right channels together made the weird resonance sound I didn't want, I was able to reproduce the effect by switching the stereo bounce I made to mono. Ick!
 
I now had a stereo track that sounded great but converting it to mono made it sound like crap. As an experiment, I panned the stereo channel all the way to the right and it sounded fine, that was my eureka moment. After bouncing around a bazillion soft synth tracks I remembered there was a split mono option in the X3 bounce to tracks dialog so I used that to bounce the track. Once I did the bounce, I had a left and right track. The left track was empty and the right track had the panned audio from the original stereo bounce. I deleted the left track and now I have a nice wide sounding mono track that I can use.
While I was using a Sylenth, this workflow should be generally usable for any soft synth with wide sounds. If you want a mono track from a stereo source without drastically changing the sound, try this:
1. Bounce the synth sound you want to stereo.
2. Pan the stereo track you bounced hard left or right.
3. Bounce the stereo track to split mono and throw away the empty track.
 
Edit: After reading how stereo pan works (balance), I realized that this approach just eliminates one of the channels. The same thing could have been accomplished by bouncing the soft synth to split mono and throwing away one of the tracks. I did end up with what I wanted but it didn't work the way I thought it did. :)
 

 
A few days ago I was playing around creating synth sounds and encountered the situation where I had stuff within a patch panning around, but I wanted to be able to manipulate the whole thing as a sound object that I could then pan around in a mix.  Just panning the output of the synth within the track didn't work well as the 'object' was way too wide and did not appear as a distinct 'thing'.
 
I haven't explored things very far, but I found using Sonar's "Channel Tools" allowed me to do what I wanted.  You can adjust the width of the synth's output then pan that where you want.  I seem to remember that inverting one channel sometimes gave better results.
 

As a general question to the OP, considering the stereo version "sounds great", why go through the bother at all?

Sanderxpander
As a general question to the OP, considering the stereo version "sounds great", why go through the bother at all?

I need a mono mix for backing tracks. I get one channel of a stereo mix, the other one is used up by the click.
 

Paul P
I haven't explored things very far, but I found using Sonar's "Channel Tools" allowed me to do what I wanted.  You can adjust the width of the synth's output then pan that where you want.  I seem to remember that inverting one channel sometimes gave better results.

I tried Channel Tools first, but narrowing things there just gave me the filter envelope sound I was trying to avoid.

Ahh. Pretty sure the issue is phase canceling by the way. You could probably solve this by using channel tools and delaying one of the tracks by a few msec.