I think you'll have the same issue with watercooling as you currently do now. I don't know anything about that case, but it looks like it isn't really designed with airflow as a priority.
By airflow, I don't just mean 'changing the fans to better ones' but also the ability for adding good fans and having those fans have adequate access to cool, fresh air.
If you put a heater in a sealed box with the best and largest fan in the world, the heater will continue to heat the box if there isn't anywhere for the heat to go. This is what happens in a case with poor airflow properties, and exactly what a convection baking oven does.
Adding fans often just moves the heat around inside, but does not provide adequate venting of cool and...