I believe that it is possible to play through multiplayer in KMod versions 2.8 and under. Although it is highly buggy and unsupported by our team. You can play it, but chances are it won't work very well.
As of KMod3 (well the 2 betas that have been released) the option for multiplayer was removed for one reason or another, really can't remember why, I just remember doing it.
I'm going to assume that you wanted to play through the game in co-op mode with a friend or 2, and as such Korax Arena isn't of much help to you. But you could try to play though KMod2.8, you might have some luck with it.