It's just amazing what the folks at Emu did to cram so much good stuff into these modules. I've been going through a friend's archive of tracks, entirely done with the Proteus 1. I have those sounds from back when I had an Emu ESI4000, there was a disc of "Emu Protozoa". Basically all of Proteus 1, 2 and 3 plus expansions. Takes up less than 40MB of disc space, and runs in Kontakt. I've been able to get all of our tracks back up in Pro Tools. Had to look up program numbers in the manual, but OMG. This is one punchy library. Then when you bring in more modern stuff like Pianoteq, those sounds are huge by comparison. Makes it quite easy to mix a track!
I think I'll be on a Proteus buzz for a while!!
For my work, I prefer having the sounds in Kontakt. It's much easier to do layering, tuning and panning than it was on the original machine. Plus, you get filters

Defo worth finding the original machine though. It has a lovely sound when things are transposed way down. Kontakt doesn't quite nail that.