Is there any way to run X with monitor resolution 832*624, 75Hz?

I installed NetBSD/Mac68k on my Quadra 800 with 500MB HD and 48MB RAM.
Tried to start x server, but got error says
"Fatal server error: Can't run X server with no screens!"
I can start X with 640*480 mode, both monochrome and 3,000 color alright
but not with 832*624 mode.  From dmesg, no "grf0" appears when booting
up in 832*624 mode.