There's many stereo phase invertors on the market so it'd be hard to say exactly which is used in the KP's, and it isn't rocket science so the engineers at Motion Sound likely just made up their own... but the biggest selling feature with the KP amps isn't just the stereo expander or any one particular feature - it's having a single, good-sounding dedicated keyboard amplifier with everything you need to pull off a gig in one box that is getting the rave reviews. As much as I like my KP-200s, it does not sound better nor have as many features as a full PA system would, and I think most other KP owners agree with that and will keep their PA's for when necessary. I don't need a large PA system for 90%+ of my gigs so the KP fits a niche I didn't know I had until I got one. It may be cheaper to cobble together a PA with all the KP has and it may even sound better when complete, but it won't be as handy or cute!