Another thing comes to my mind right now, I have different p96mode-settings files for each monitor driver (set by tooltype "P96SettingsFile" or something). I thought that is a good idea, and I was afraid to delete anything good, which worked nicely with the voodoo. Perhaps there needs to be one p96settings file only (used by both monitor drivers) ?!
Yes, I did have settings for 3 monitors in the same settings file - but best to check that the settings do fit for both cards.