It really depends on your ai for your 6 boxes. Theoretically, it is possible as a 6 mage. But practically, it is not because you kinda need to be very agile when there are adds or your script is so good that you can chain cast pet to always have a pet that will aggro the mobs. Regardless of your choice, for a 6 mage box, you will have to designate a pet that will always be a sacrificial tank, and then the rest of your ai needs to move AWAY from the mob so that your 6 mage are not targetted by mobs even if your pet is able to maintain aggro.
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Agreed with what the others have recommended, if you are very much into mages (i did the same thing), here is what i would recommend:
4 mages (send pet to gain aggro, recommend two pet tank , and two dps pet depending on what you hunt)
1 Shaman (best buffs for pets, slow mobs and heals you and pet in a pinch, dot heal, nuke/dot during emergency or named npc with big health)
1 enchanter(best haste for pets, for the mind buffs on 4 mages, nuke to finish faster if mana allows, tash to help shaman slow faster if needed)/
-Bard is my second choice because you kinda need to do a lot during crowd control and you still cannot heal very well. Your mage can heal your own pet.
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==SOMETHING TO THINK ABOUT==
Now... having said that, you can still do the 6x mages if you have a high level shaman not in your group because your shaman will never be dealing enough damage. Same with the high level chanter.
I personally will have two other casters like a wizard or bst to round it up and best caster synergies. (BST crack plus enchanter crack)
However,.. if you are gonna have THAT many buffs, you might as well just have two mages with pets as tank to draw aggro and 4 wizards to pew pew kill stuff quickly; plus the high level shaman + chanter +beastlord outside the group helping(buffing, slowing, crowd control, healing)..... That would be a white glove service... Haha, sorry, i went crazy....