I have a newer 2013 Mac Pro. I run my main 30" monitor off of Thunderbolt. I also have a 55" Samsung running off of an HDMI port. When i start my computer it always thinks the HMDI monitor is the 'main' monitor. I go the System preference and set it up so the 30" is the front left monitor with the dock, but everytime I restart my computer, the 55" HDMI monitor is the front monitor with the dock. So when I start the computer I have to always go to the System preferences and have to change it back so the 30" is the main front monitor WITH the dock. Does HDMI always take preference on a MAC trashcan? I'm running 10.10.5 Yosemite on this computer because it is used in a music recording studio and Yosemite is the most solid for our set up. Thanks for any thoughts on this.