The only good thing about the Khorn is the tweeter horn, the driver is crap, and the bass cabinet resonate in all kinds that it shouldn't. But that tweeter horn is great for it's type, and designed by Electrovoice. It inspired the later (and way more legendaric) K501 and K402 horns that are considered the best. But the Khorn itself will never be a great (in the sense of technical advanced) speaker, it has to many fault's in it's basic design to be able to fix it. Better new from start and design a speaker that looks as it but is technically on point (but that require skills).
But if you just want to mod a bit with it, Volti audio, ALK engineering and Crites Audio are the most popular modders, who's kits seems to be popular. But those will never make it a great speaker, because they don't fix the faults int the basic design.