I've been playing Hexen on skill 5 for the last 3 years myself and dying only when accidentally falling into an abyss or so, but I'm positive Korax Mod can't be won on skill 5, at least not with the Fighter. It might be though that it's possible in Korax Mod II as all 3 player classes became more powerful.
Anyway, on skill 5 the cheats are disabled, it's coded this way in Hexen and we left it so.
As for Deathkings, you can buy it online from CDACCESS, either as a standalone box for $9.95 at http://www.cdaccess.com/html/quick/hexendkpr.htm
or as a package together with Hexen and Heretic at http://www.cdaccess.com/html/quick/hexenbunpo.htm
Playing Korax Mod or KMOD2 in Deathkings? Technically, it's possible, no prob. The question is game balance, it was never tested and the whole RPG system of the 2 mods are optimized for the game flow of the original Hexen maps. As there are big tough monsters already at the beginning, you'll advance up the levels faster, OTOH it's a good Q whether you'll survive that far at all, especially with the Fighter. But you're free to try it and share your experiences with us... [img]images/smiles/icon_wink.gif[/img]