First of all, i apologize if i didnt understand everything in this thread here and i hope that i can contribute something, but i would like to share my experiences.
I did get a Nvidia card working in a standard PC setup (no laptop) with Soft15khz and Powerstrip and i didnt need a dongle. It was a old 7800 GS AGP card and this was my first steps into a 15khz arcade-setup. The moment i read about GroovyMAME, i changed my setup to ATI
I also tried to get my laptop running. Its a hybrid Intel-Nvidia setup with Optimus technology, which is bad for GM because the Intel-driver manage the output resolution. Trying to find a solution, i found this tool: http://www.clevertec.co.uk/productsfree.htm#dtdcalc
With that tool, i could manage to "inject" only super-resolutions into the Intel-driver (and only 6, i used 5 because i needed one native resolution for my laptop screen) with the help from SailorSat. It worked quite well for MAME, but not for the desktop or other apps like VLC and similar, because they didnt handle well the super-resolutions.
Here is a example how the destop screen looks in Linux, just to clarify what i am talking about: http://www.arcadezentrum.com/forum/index.php?attachment/26934-intel-1200x300-jpg/
I dont know why, but i reverted everything and since then i didnt try any further to get 15khz working out of my laptop (sadly
But this thread and this CRU tool sounds somehow promising and i think i will try it again. My biggest hope is, that guys like pakoman or Calamity, will maybe take a look into my provided link, as DTD-Calculator was at least a way to get Intel-Nvidia setups with Optimus technology (or onboard Intel) working with 15khz CRTs. It would be just great, to get those laptops running with GM, as we would have mobile arcade setups
Modelines used with DTD-Calculator:
modeline '2560x224-15khz-2560x224-15,72kHz-60,0Hz' 48,418 2560 2632 2864 3080 224 238 246 262 -hsync -vsync
modeline '2560x240-15khz-2560x240-15,72kHz-60,0Hz' 48,418 2560 2632 2864 3080 240 246 254 262 -hsync -vsync
modeline '2560x256-15khz-2560x256-15,72kHz-60,0Hz' 48,418 2560 2632 2864 3080 256 254 262 262 -hsync -vsync
modeline '2560x288-15khz-2560x288-15,72kHz-50,064Hz' 48,418 2560 2632 2864 3080 288 296 305 314 -hsync -vsync
modeline '2560x300-15khz-2560x300-15,72kHz-50,064Hz' 48,418 2560 2632 2864 3080 300 302 311 314 -hsync -vsync
One important thing is, to NOT use the clone mode, because it expects that both screens can handle the resolutions. You need to use the extended desktop mode to get everything working right.
Hope that helps a little, since i last tried this stuff 4 years ago.