20MK a level.
Use of Ki at Level 2.
Ki Transmission at Level 3
Inhumanity at Level 4
Zen at Level..... crap.... 7
(Although you could slap Ki Healing in there at Level 5 and still hit Zen at 7).
But yeah.... you want Zen at 6? It's Use of, Inhumanity and Zen. That's your lot.
(But holy crap, how good is your skill if you're planning on needing Zen by Level 6?! Especially because the mental attributes can go over 10 without even needing Inhumanity. Zen is 440. Damn. Taran's either REEEEEEALLY good, or utterly delusional. I'll let you pick.)