how do you stack a 3 tiered cake on top of small 6" round cakes all around it?

Here's a previous thread on stacking with satellite cakes:

http://cakecentral.com/modules.php?name=Forums&file=viewtopic&p=6956272&sid=b0304fe154e6da468f7e5907f12d683a

HTH

You treat them like any other tiered cake by using supports in all lower cakes.

In this case, the 6" base cakes will only need supports in the portion that is directly under the above tiers.

Spread out your 6" pans, 6" dummies, or 6" paper templates to measure the empty space that will be in the middle of your 6" circle of satellite cakesonce you know what space will be available, use that size dummy in the middle to help support the rest of the upper tiers.