imo, running 2 sponges does work very well but I think using one sponge and the new biomax would be just as good. as for the sponge on the intake...I do something similar on the tank I keep my trimac in. reason being is I hope to one day show him and don't want him scratching himself by ramming into the intake if he gets startled. it does also help a lot of the gunk from getting into the filter. 
