So, the TRS jacks on the back panel are mults of analog out 1+2. If you are using those for your monitors, then you can't have a different level or mix for the headphones on channel 1+2.
You could use the front-panel headphone out for one set of headphones, or you could move your tracking room headphones onto Outputs 3+4, and 5+6.
I think that addresses what you are experiencing. If not, please follow up here or open a ticket with support so we can help you get your setup working...