I read in another thread that Exporting audio is purely math and does not rely on the audio interface at all.  
 
However, that raises an interesting question / observation for me...

I just got a Focusrite Scarlett 18i8. When I went to mix down in CbB, I got horrible audio. (It played just fine in the software before I mixed it down). And no, it wasn't clipping as I limited it.
 
However, at this point, I changed the buffers in the Focusrite to 1024 and Exported again and bingo. It mixed down just fine...no glitches. For fun, I put the buffers back to 128, more scratches and pops.
 
So, if this doesn't use your audio device, can anyone help me understand what is happening here?
 
I should also throw in this tidbit...Doing the same test in Studio One, there were no pops and clicks at 128 buffers. In other words, I don't have to adjust the buffers to mixdown in Studio One.
 
Also, I'm doing a "fast mixdown" in Sonar, not the "real time" mixdown. (So in other words, the default type of Export audio)

Try increasing BounceBufSizeMsec in Preferences > Audio > Configuration File
 
 

Another interesting fact...Cakewalk cannot mixdown without a soundcard.  As an experiment, I turned off my focusrite, then loaded Cakewalk and got the expected "No audio device" error.  I then did a mixdown, which APPEARED to work, but only provided a 4kb file.  So, I have a friend that did the same thing...just as a test...only he has Sonar...not the new Cakewalk.  Same exact thing happened to him.
 
So, then I tried Studio One, and after getting the same cute little no audio device errors, I went ahead and mixed down...got a full fledged file that mixed down perfectly. 
 
So, I'm not sure I agree that Cakewalk / Sonar doesn't utilize the sound card for mixdown as Noel once stated. 

And I'll try your suggestion as well scook.  Thanks for that. 
 

Without knowing a lot about the internals of each program, I am not sure what conclusions can be drawn by these types of tests other than the DAWs are different.

Oh, I agree.  Honestly, I want Cakewalk to work for me.  I know the workflow, and I love the MIDI editing capabilities.  But with the mixdown quality I was getting, I was concerned.  I will definitely try your suggestion when I get home work this eve.  Thanks!

You don't need an interface or even a sound card.  You just need an audio output (real or not real, can't think of another word for fake).  I have Reaper installed on the same machine as SONAR/CbB and can create a mixdown file just by selecting one of those phony outputs created by Reaper in SONAR.  Just make sure your Master output is set accordingly (not that I know you have Reaper installed too).
 
Hit back to discuss further, if desired.
 
Kind regards,
 
tecknot

My guess is in the absence of the Focusrite audio driver the Software will revert to your on board audio cards driver and use that. Sonar has always been a bit finicky about this. Not a problem for me as on my main DAW I don't even install on board audio drivers. I have an interface and that's all I've ever used. And I perform hundreds of mix downs monthy and I have never had them not be exactly the way it should be. I just use the default setting sans the change to 16 bit. My buffers are always the same at 128. I never touch them these days. 

The export options in Cakewalk are more comprehensive than some other DAWs. This leads to confusion for some users. One of the options for audio export is the "Source Category" which includes Tracks, Buses, Hardware Outputs, Entire Mix and Clips.
 
It sounds to me like you have Hardware Outputs selected in this field.
 
I usually bounce my mixes to a track and then export the clip.

Base 57
The export options in Cakewalk are more comprehensive than some other DAWs. This leads to confusion for some users. One of the options for audio export is the "Source Category" which includes Tracks, Buses, Hardware Outputs, Entire Mix and Clips.
 
It sounds to me like you have Hardware Outputs selected in this field.
 
I usually bounce my mixes to a track and then export the clip.

Base, you nailed it.  Doing a mix to a bus, and selecting Master solved it.  Thank you!  

@Cactus Music:  I do not have onboard audio.  I built my machine from the ground up, and the last thing I wanted was onboard anything.