alright. in that case, i'd recommend either 171 ar6s or 171 anthems.
they're both on the softer side, but the ar6s are a little stiffer.
my friend has anthems, and really likes them, and i have ar6s and absolutely love them.
they're both good skis, and slay park. haha
I would go with something a little bigger personally like the 176 range. Armada makes good skis, line makes cheap good skis. Or you could always check out some independent brands.
he's only 5'9 though? I'm 6'3", 185lbs. and I ski a 179-181 don't you think a 176 range would be a little long for 5'9 150lbs. i'd say something around 170 would work nicely but I guess its personal preference.