When booting with a single card, Nvidia 9800GT 1GB, the GraphicsEnabler works great. Both DVI ports work fine.
When booting with two cards, the 9800GT above, and an 8800GT 512MB, I get a kernel panic after both ports on the main card are initialized. I can tell because the LCDs indicate they're both getting a signal, and then poof, kernel panic. Hold reset to reboot thing.
Is GraphicsEnabler designed to recognize dual video cards?