BootX ignoring video parms?

I'm using YDL 3.0 on a Beige G3 Power Mac.

It seems as if the video parms I enter in BootX are ignored. I start out
in Mac OS with a resolution of 1152x870, 75 Hz, thousands colors. No
matter what I enter in the kernel args window, when the screen goes
black, I get a few lines of readable text ending with "arch:exit" and
then the screen resolution changes down to some very low value just as
the yellow-colored YDL logo shows up and the image turns into lots of
horizontal dashes, unreadable.

The problem is that I'm using a Sun/Sony monitor (GDM-20D10) that cannot
support the low resolution, so it loses video synch and I can't read the
screen. A different monitor (that can handle the lower res and rates)
works fine, but I can't use it permanently.

I'm circumventing the problem by adding a "5" to the end of the BootX
parms to force run level five (so BootX is listening to *some*
arguments, at least). After all the boot stuff is finished, I get the
graphical log-in screen and can do "startx"; X and KDE run just fine.
But I'd still like to be able to read the screen in non-GUI mode.

I need to stop the boot-time reversion to a low resolution. I've tried

"video=atyfb:vmode17:cmode16"

and various substitutions of numbers, but nothing changes.

I read somewhere that "video=OFfb" would keep the Mac OS parms, but that
didn't work either.

Any suggestions appreciated. I'm a Linux newbie, so be gentle.

thanks, Isaac