Is it supported by MorphOS? So far I've not been able to get to.

Am I in the wrong forums or something? :)

No, you are in the right place, but only a very few users own an eMac and I don't know if any of them have tried to use the mini-vga/dvi port to run another monitor.

IIRC, one person tried before and found that it did not work, but I could be wrong. Have you even tried to use an external monitor connected to the mini-vga/dvi port?

I gave away my eMac at the last AmiWest show as a prize to the winner of the Amiga Game Competition, so I don't have one to test.

For more immediate answers than here in the forums, you can try the IRC channel where most of the MorphOS users and developers hang out. I don't visit there often, as I am not a regular IRC user, so I don't remember the exact name of the channel, but I am sure it is listed somewhere here on MorphZone.org, or on the official MorphOS developer site.

Have you played around with the tool types of the radeon driver? Maybe a DVI_ENABLE= NO helps, dunno about the option FP0_ENABLE, maybe it does somethig in this context.

eMacs have some analog mini vga connector port to connect external (analog) vga displays. I never really tried it since I didnt have the required mini-vga to vga converter cable to connect a monitor at the time I had an eMac for testing.
The Radeon driver tries to output the current video on all output ports. If it works on eMac at all, you will get identical sync & resolutions on both the internal crt and external monitor.

I tried it once and my monitor gave me a signal not supported message...

Will try to tinker around a bit as Zylesea suggested. Thankx.