StereoFXDemo was my take on a stereo widener in 2007. It has several tricks worth noting.
The Stereo Wide control doesn’t simply amplify the side channel, it distorts it. It applies a transform designed to bring sound energy forward in space, so boosting it will produce a hyped, wideness effect. The current-plugin equivalent is Wider, which does this in a much smoother, more hi-fi way. StereoFX does it more aggressively than that.
Mono Bass highpasses the side channel. That’s a similar behavior to today’s ToVinyl. Using it, you can tighten up stereo bass.
Center Squish is something not quite provided by any current plugin, unless you count doing things with EdIsDim. What it does is this: applies a saturation to just the mid channel, in a way that does NOT boost it, just makes it run out of juice and begin to distort. The sonic result is that you get an overdrive effect that widens. Using Wider in the same way, what you get is a center boost that tightens imaging or a center cut exaggerating wideness and depth, but using StereoFX Center Squish, the center drops back to become more driving and distorted. A one-trick pony but unlike any other plugin, so if it sounds like you’d like it, check out the demo.
If you want this plugin, buy Wider or ToVinyl (both plugs which carry on the lineage of StereoFX) and ask me for StereoFX in email. I’ll send it to you.