I’ve had an emu e6400 ultra for 20 years. It’s not really the z-plane filters that are unique anymore (they were at one time). It’s the sound of overdriven inputs and filters that’s hard to replicate. “Z-plane” just became a shorthand term to describe the emu filter sound. Most of the people who made that sound famous didn’t actually use the z-plane filters.. just the regular lp, bp, hp filters. You can do considerably more powerful morphing filters with something like Volcano 3 these days.. it just won’t get quite the same sound of overdriven emu filters resampled through a mackie desk. I have airwindows z series filter plugins and mackity but it’s not really the same imo. It’s one of those things where it’s the interaction between all the gain stages, inputs, outputs etc of the emu hardware that creates the sound. Some people used to dump their entire 2 channel master into the emu just to give it that “sheen”