What Hardware is needed to use multiple Yeti USB Microphones in Adobe Auditions?

This isn't a hardware issue you've got - it's that you need a means of synchronising the digital outputs of multiple USB microphones. If you are talking about a Windows machine, then your only option is to use the (free) ASIO4ALL driver, which should let you aggregate your USB mics so that they are all available individually. What this does is take one mic as the 'master' source and syncs the outputs of the other mics to it, thus avoiding all of the clicks and loud crashing noise you'd get if they weren't synchronised.

It works (well it seems to for most people) but it's far from ideal. Invariably using a mixer and 'normal' mics causes a lot less trouble.