I picked up the free widener plug called Sheppi Spacial Enhancer some time back. I believe Bitflipper posted that link many years back.
http://dallashodgson.info/articles/OpenAmbienceProject/ However, the folks up top are correct. If you use a widener plug to "widen the mix" you WILL be sacrificing the quality of the mix. I have used the SSE plug in the master bus and yeah, it sounds cool in the studio, BUT..... set there while the music is in playback with SSE turned off. Everything is nicely defined.... plenty of kick and punch in the music, nice full sound. Click to turn on the SSE and much of that drive disappears in the process.
It is much better to use panning and doubling to get the width in the mix. I often record my acoustic guitar 2x and simply pan the tracks 80% to 100% opposite each other. The slight differences between the 2 tracks gives a nice wide stereo field to the mix and everything else can pretty much stay really close to centered. Since the guitars are both playing nearly the same thing you don't end up with the weird 100% panned feeling. I also tend to pan my BGV wide as well, with this adding width to the vocal track harmony parts.....and they are at a low volume level so again you don't get that distinct feeling of extreme panning.
If you want the lead vocal (mono track) to have a fat, wide sound..... I record an identical vocal track for the lead 3 times. I pay attention to the singer's annunciation, timing, and groove and make sure the 3 tracks are as close to perfect with each other as is possible. Words, phrasing, etc...start and end together and in between as well..... One track goes up the middle at lead track volume and the other 2 are 80% or so panned opposite each other and way down in the mix somewhere around -16 to -20 db normally. ..... to the point that you can't really hear them clearly unless you solo the vocal bus.
If you have proper panning and good technique in the mix, the widener plugs are not needed.
Having said all that.... I do use the SSE from time to time for it's overall ambient sound.