ATOM-15 seems to cause issue with Dual-Monitor Setting

Dear all,

I already posted this question in the arcadecontrols forum and I hope it is ok if I give it a second try in this forum which seems to be the better place for such questions. I will also try to give more details here.

Here's my Problem with ATOM-15:
In my cabinet I use to screens. One CRT as the main screen and one LCD as a dynamic Marquee. With an ArcadeVGA5000 it just worked well. 
Then I switched to a Sapphire Radeon HD 6450 GPU with CRT EMU-Driver and this also worked well.

Finally I flashed the bios of the GPU with Atom-15. When booting the PC with only the CRT connected, there is no problem.

However, when I have the second screen connected (LCD-Screen used as as dynamic marquee) the CRT seems to loos the signal after the first seconds of booting. There will be no picture and I do not know, if it continues booting and running windows. The Windows bootscreen won't appear.

When I unplug the second screen and restart, it works again. After everything is loaded, I can plug in the second screen and the dual monitor setting works.

Any help will be highly appreciated.

My setup:
ASUS Z87-A Mainboard
Intel Pentium G3258 CPU
Sapphire Radeon HD 6450 GPU with CRT EMU-Driver, flashed with Atom-15
Windows 7
Sony Trinitron CRT as first screen
Stretched LCD as second screen
GroovyMame (version 0.214)
AttractMode (version 2.6.0)

Best regards
Max