The OP mentions doing a null test. Depending on how it was exported, there could still be variations in the project files (i.e., master fader), but if the same project file was loaded into both they should sound identical when playing the project file alone.

What you hear playing a project inside SONAR isn't necessarily the same as what SONAR will render.  The real test requires using a second recording device (another computer/recorder) and record what comes out to the speakers when you play the projects (record the signal sent to the speakers, not the sound out of them).  And compare that.  Of course getting that to null (due to timing) might be tricky.  I suspect there may very well be a difference between what it sounds like real-time in the DAW and what it exports as.

I believe S6 was 20-40% better than S5.

I could be wrong but I believe the Capstan rollers in Sonar 5 were higher quality than Sonars newer versions.
thus less wow and flutter .

mettelus
The OP mentions doing a null test. Depending on how it was exported, there could still be variations in the project files (i.e., master fader), but if the same project file was loaded into both they should sound identical when playing the project file alone.

yeah, sorry, brain fart, although he doesn't say he mixed them down after inverting and inspected the result, rather that when phase inverted there was silence, which could mean something so quiet it seems to be silent... dpe was only introduced in s5 so it wouldn't be a huge leap of logic to consider there was maybe some improvement/change between versions, and dpe is known to cause issues with some plugs etc
/fwiw/ymmv/hth/goodluck, etc :-)

If listening isn't enough what's the right way to be certain then? Should I take the two rendered files and re-import them into a project, phase invert one of the tracks, and then bounce out again and inspect the result visually to make sure it is dead flat-line?   Or is doing this going to potentially introduce something new that may only confuse the results?
 
Sonic

Why care if there is an actual difference or if it is confirmation bias. I think you should trust your ears. Use what sounds best to you and make music. Life is too short for a musician to waste time on this kind of stuff.
 
S6 was an improvement over S5 in a lot of ways.

Think of it this way, no matter what its only in your mind you can attest too. Explanation or not, teach yourself to hear more. Use the processors and the mix to try and make one sound like other. Its great if only you can hear it, you may be onto something.
AMK
 

chuckebaby
I could be wrong but I believe the Capstan rollers in Sonar 5 were higher quality than Sonars newer versions.
thus less wow and flutter .

A little alcohol and cotton swabs might help to even the playing field, Chuck.

fantini

chuckebaby
I could be wrong but I believe the Capstan rollers in Sonar 5 were higher quality than Sonars newer versions.
thus less wow and flutter .

A little alcohol and cotton swabs might help to even the playing field, Chuck.

Aint that the truth
 
I used to have an endless supply of both. Along with a bottle of sewing machine lubrication (For rollers, gears).
And the demagnetizer (which I had to buy a new one a couple years ago). Those are not easy to find any more. A good one anyway.