Differences between TripleHead Analogue and Digital

Hi there - not strictly a Catalyst question, but related to a couple of Catalyst systems I'm putting together.

I have four MacMini based systems, using various TripleHeads. MacMini >> TripleHead >> three monitors. Some of our TripleHeads are analogue VGA and some are digital (DVI). For the purposes of this, everything is being converted coming out of the TripleHead and run as VGA.

With an analogue triple head, my MacMini will support 3x1024x768 outputs. However, with a digital one, it will only support 3x800x600. Even using the Matrox software to load only the 3x1024x768 profile onto the TripleHead, it still will not support an output this size.

Does anyone have a workaround for this? It seems strange that the Mac will support a larger output over analog than digital..

I'm running 2.66Ghz MacMinis with the NVIDIA GeForce 9400M graphics card (MiniDVI & ADC), and the Triple Head plugged into the MiniDVI port.

Thanks