The S1 is Wave's attempt on a Blumlein shuffler, which separates the bass frequencies and introduces a polarity shift to "widen" the lower region without affecting the rest of the signal.  Though they do not do it via a polarity shift like Blumlein proposed, but rather an MS gain control for the bass.  I have attempted both methods manually, and I have to say the Blumlein method is far more pleasing.  One problem with the S1 is that is also uses a rather hum-drum EQ to separate the bass and that colors the sound and introduces extra phase to the signal.  It could do with a modern update IMHO.

∞

∞

I have been getting a lot of joy from this free plug in:
 
http://www.kvraudio.com/p..._open_ambience_project
 
It is a free plugin and I have been using it quite a lot on mono acoustic guitar tracks. I have been mixing a project for a singer/songwriter and she is tracking everything at home and sending me the multis to mix. She is making nice acoustic guitar recordings but totally mono. I have been looking for ways to widen these tracks.
 
This is mono to stereo widener for your info. But it seems to work very well and it collapses very well to mono too. There does not seem to be any timing or delay issues with this either. It is subtle effect but also very noticeable if you switch it off sort of thing.
 
I have not tried a whole mix though it and I don't think I would anyway. I am very particular about what I put entire mixes through. We all should be. People are in far too much of a hurry to put an entire mix through something dumb and stupid and in the end the mix goes pear shaped! At first it sounds like it is better but then after careful listening you will find it is worse.

mike_mccue
S1 Imager seems to delay the signal of one channel so that the other channel may take precedence.
 

 
Though I didn't post it before, I did a quick seat of the pants calculation and it looked like the phase change in the pictures from your test might equate to a distance of roughly 8 inches or so. I found that curious as it sort of puts it in interaural delay territory and I wondered if that was a coincidence or not.

the s1 always sounds like clownphookery to me

∞