Originally Posted by Scottrik

You certainly CAN run 6. I prefer to run as many as possible (12 in my case) because to get the "grip" you need (minimal slip) it requires less clamping force be applied to 12 balls as 6 (maybe half? I don't know the engineering here). Less clamping force generally means a smoother diff action and less pre-load on bearings. I'd also guess it would be easier on the diff balls themselves and diff rings, though that's more intuitive than well thought-out.