I have 2 identical external brand new JVC 28" monitors displays which still wont work, but Ive discovered that by swapping one of my JVC monitors for an old 28" Acer everything works. It's still a bit flaky in as much as sometimes I have to reboot to get all 3 displays to come on but then they all stay on.
Ive also noticed that during start up don't immediately enter your password or show your face until you are sure the machine is up and running, in other words wait 60 seconds or so before showing your face or entering your password. When I do this coupled with the mis matched monitors then 9 out of 10 times everything fires up perfectly.
One other thing that improved stability for me was changing power settings to never turn off display when on mains power.
With all of that being said there is clearly an ongoing problem and its a pain that MS seem incapable of fixing it.
Hope this helps some of you
Steve