I usually run my phones in mono as the aux sends on the console are in mono and to set up a stereo mix uses 2 sends. I have had one complaint in 15 years from someone who wanted a stereo headphone mix, (I think he was trying to big note himself in front of the band coz they were recording with me and not in his own home studio). I suggest to a lot of players that they only use one side of the headphones anyway when a lot of the band are tracking together so that they can hear their own instrument clearer, not in the headphone mix.
I usually have 2 different headphone mixes available I can set up 4. I have a 4 channel headphone amp that can take any of the 4 aux sends and have independent volume treble and bass controls. Each headphone amp channel can also take a mix of 2 of each console aux. I can run up to 4 sets of phones on each channel of the headphone amp (if needed) that's a possible 16 sets of phones. I do start to scrape the bottom of the barrel with which phones I have when more than 8 pairs are needed, which is almost never.
How it works, 1 mix would have more rhythm section, drums. Bass, guitar with a little vocal and whatever else is going on. The person doing vocal or guide vocal or other stuff gets a mix of louder vocal and what ever they want to hear.
When you have a band of 4 or 5 together it's nearly impossible to get the headphone mix right for all of them, only last night the singer doing guide vocal wanted more and more vocal in the phones, until all the others told him he was deaf as the vocals on that send were unbearably loud.
Mostly my setup works.
Alan