I have an Apollo, but what I have is a setup both in Logic using two busses (one for the entire mix, and one for the record enabled track) which I send out of my aux monitor outputs to a Mackie headphone amp. That way my singers can control their own headphone volume, and then I can control the levels between them and the mix to their taste.
It sounds a bit complicated, but once you have it setup you can save it into a template and recall it when you need it.
This is a pretty cool video that has some great ideas for setting up headphone cues
https://youtu.be/zHYF_-My5NY?t=265