Hi.
I have the Studio 1810 also and have found that I need to access universal control on a pretty regular basis to keep things going. If you open it and select your 1810 it will either show bypassed (on seemingly random days) or the regular mix window (un-greyed-out). If you press the "reset" button (upper right) you will regain control and can then select the mix 3/4 button and then the "mirror main" button and, as I do, the 5/6 button and "mirror main" also. I have two sets of headphones. My recording, closed back, set I use during tracking is on headphone 1 and it mirrors the main. My open-back reference headphones I have on headphone 2 and it mirrors 3/4 and I use it to reference the mix to eliminate any room acoustics issues and validate the mix. I also have, on occasion, monitors set on 5/6, or a headphone amp for a group, or when I need outs for podcasting, broadcasting, etc. When I first got the interface I complained to Presonus tech support on a regular basis, but am now more in touch with the interface and, while I wish I understood better how to lock in my settings, I at least can get what I want each day and do professional work with it. One more tip, I have universal control start on login so that it is always available for me. That helped remove some friction. Good luck with your projects. -Ed