Hi Matthew,
All ME-1 and ME-500 units in a system share the same sources. So if you patch your Aux mixes to the ME tab, all mixes will be available to all units.
On ME-500, you could simply leave all Aux mixes muted apart from the one you need, per unit, but you’ll be wasting a good part of the 16 keys doing so.
On ME-1, you can choose to ignore all Aux mix sources apart form the one you need, and still use the other 15 keys for single channel direct outs if you like.
Both were designed for the user to create their own mix, rather than take a mix from the console. If you are planning to mix monitors from the console, but want to give a degree of control to the musicians, then the SQ4You app is a better, more economical, and IEM friendly option.