bitflipper
I agree, that is one of the coolest interfaces ever. I just never considered it because a) every stereo enhancer I've ever tried was lame, and b) it's a hundred bucks. I might have to try the demo, though, if you're that happy with it.
I tried the demo, within about 30 seconds said to my self "hmmm, very natural sound, no funny phasiness", fell in love w/ the interface, and about 45 minutes later plunked down for the Stereo bundle, which I think was on sale at the time. I actually planned on getting Monofilter only… It's certainly not cheap, but I think when you try it you might be impressed with what it can do.