Hi.
The mediator use gfx mem on the gfx card as DMA buffer for the ethernet card.
I have a A4T with mediator, voodoo 5500 and a cybervision PPC installed.
OS is 3.9 with all updates. and use picasso96 and the voodoo card as main display.
As there is no picasso96 support for the cybervision ppc. I have too have a second system on another HD if I want too use cybervision PPC installed with CyberGraphX package.
(there is no CyberGraphX support for the voodoo card)
But I have no problem with both card (hardware) installed in my A4T.
This is just for info. I do not have any clue to fix your problem. sorry

Sorry for my bad english.