What would you add to this group?

[Slave]

I too have to go off the path here a bit and just say, if the SK became a Warrior, well, they tank better (best) and do more damage. He will also level much much quicker. That's basically all the utility you need in a tank when you have a monk in the party too.

The ideal party makeup as the OP described would otherwise be:

Dark Elf or Halfling Cleric (for Hide/Darkness Necklace or Hide/Sneak)
Dark Elf Enchanter (for Hide)
Iksar Monk (for better survivability)
Barbarian or Halfling Rogue - best stats vs best exp
Ogre Warrior with all points in Dexterity
Troll Shaman of Innoruuk with all points in Stamina

Basically the only things you don't get with this is ports. (Oh no, 100pp!) Use damage shield potions on the warrior at higher levels.