Hi,
You've been doing a lot of research and finding answers. Looks like I'm late to the party.
A dual DVI card is difficult to find for your uses, the ATI 9600 PC/Mac Edition does have those features.
But I must warn you that these 9600's have had difficulty in some G4's. In some Mac's like yours they work fine, in other's - a blank screen. It's worth a shot, just as long as you can return it.
This ATI Support Document tells the story:
https://support.ati.com/ics/support/default.asp?deptID=894
Then type 737-21888 into the 'search' window, hit Enter.
Edit: If for some reason that link won't work, I'll insert what it says:
737-21888: Radeon 9600 PRO PC & MAC Edition list of supported system configurations
The information in this article applies to the following configurations:
Radeon® 9600 PRO PC & MAC Edition
"Quicksilver" Power Mac G4 model
"Quicksilver 2002" Power Mac G4 model
"Digital Audio" Power Mac G4 model
The Radeon 9600 Mac & PC Edition is not compatible with the "Quicksilver", "Quicksilver 2002" or the "Digital Audio" PowerMac G4. If a Radeon 9600 Mac & PC Edition board is installed in one of these systems the result is a blank display.
For assistance in differentiating Power Mac G4 models, please refer to Apple Article 58418.
Let me know what happens.
Regards,
Dave