Every time I open X3 it opens on my 2nd monitor. It doesn't matter how many times I move it back to and maximize it on the main screen, it will not remember that position the next time it opens. Annoying!

Looks like the forum is gone weird this morning.. just text?
 
Any how may I ask if other applications behave the same way, or only Sonar.
Only thing I can think of is the second monitor has become #1. But if other software is opening on Main screen then this would not be the problem.

Yeah the forum has gone screwy for me too. It's been stripped of its CSS. 
 
Nope, no other apps are behaving like this, they're all opening on the main monitor as usual. 

I wonder if you disable the second monitor in your graphics control panel. Then open Sonar, if it will force it back.

Interesting idea, but unfortunately it didn't work. Disabling the 2nd monitor of course forces X3 to open on the main screen, but as soon as I reenable the 2nd monitor, it opens on that one again. The Sonar splash screen appears on the main monitor while loading, but the app itself loads on the 2nd screen. 

Which one is labeled the primary monitor in windows? From my angle I do hope Sonar X4 will contain a few enhancements for multi monitor including the ability to drag and drop multiple multidocks for each monitor and save the layout via a screenset.

The main monitor is correctly labeled the primary monitor, I double checked. Plus all of my other applications are loading on this screen by default. 

Happens with brand new projects?

Also try starting it up with 'run as admin' or vice versa.

Do you use screen management software? I use DisplayFusionPro (which has a great freebie version BTW).
 
You can force an application to open on a screen with that. Have you inadvertently done something similar?