I have the Maximizer diffs, They have an aluminum cup and 3mm screws. The screws are like twice as thick as the stock screws so they are much stronger so you won't shear the heads off. You do not need different cases to run these diffs, you can use the stock cases. Aluminum cases are more rigid and will keep the ring and pinion gears from losing mesh as easily, although I've never had a problem with the stock ones. As far as diff fluid, that goes in the diff cup to slow down the diff action. You can use it in the Maximizer diff cup, but it may leak out with time. The solution would be to put a thin layer of silicone around the rim of the cup when fastening it to the ring gear. You don't want to fill the case with diff fluid, because all that would do is slow down the power to the wheels. And you should always at least use some grease in the cup and ring/pinion.
The Maximizer diffs are the same basic design as the stock diffs, but they are much stronger. You can use them for anything you want to do.