I promised myself to not post here any more. But just one question: how much memory you leave available in the Radeon tooltypes?
Remember that the Mediator needs some of the video card memory to act as a buffer for the rest of the busboard. So at least 1Mb must be left for the other cards in the system.
A 64Mb card must be set to a maximum of 63Mb. But the less, the best. Set the tooltype to 15Mb and the remaining memory will be added as FAST RAM (15Mb to video modes, 1Mb for the Mediator buffers, 48Mb for the system).
If you set all the card's memory to itself you'll have those lockups as soon as you choose a RTG resolution.