Can X2 User Open X3 File?

I am an X3 user planning to collaborate with a X2 user.  I know Sonar 8.5 users can't open X3 files, but I was wondering if X? series users can open each other's files.

Thanks Mettelus,
 
I'm wondering if basic MIDI features, like the Drum Map Mgr would remain in tact.  BTW, can you explain "stem" files?
 
Thanks,
KC

I misspoke because I originally grabbed the wrong file! The VST3 effects cannot be loaded into X2, but the tracks are indeed all there, so you may be able to collaborate, but I would definitely create a project with X2 in one name and X3 in the other.
 
Stem files are audio mix downs of tracks. In the export audio dialog, after selecting tracks you can choose "Tracks" instead of entire mix, and the files save with "[name you choose] - [track name] - [track #].wav"
 
But now that I grabbed the correct project, you may be able to share the project folder, but not sure of any issues (other than X2 cannot see X3-specific features). 

Swapping files back and forth between versions should not be a problem so long as the user of the newer version doesn't rely on any features not present in the older version. It's possible one or both of you would encounter some minor weirdness with the persistence or appearance of certain GUI features (take lane order comes to mind), but I wouldn't expect any major problems.
 
Incidentally, 8.5 can open X-series projects just fine; you lose big features like Prochannel and elements of the Skylight interface like the Multidock and Screensets, but, again, if they're not used in the newer version, it's not a problem.

Or you could exchange wav or MP3 reference tracks.
In my experience with collabs, sending the entire project would have been major overkill.
You may have something different in mind, but generally, it is not necessary.