I've got a Tetra Whisper AP 150 running two sponge filters and one airstone, and it's supposed to handle up to seven such outputs. I get very good air output, almost too much, even though one of them runs through four feet of airline (at first I was too lazy to cut the line to size, and then I realized, why not stick it at the other end of the tank and improve circulation). It's also much quieter than the inexpensive little air pumps. But it also doesn't cost an arm and a leg.
Try getting an airline kit with Y or T pieces and individual valves. I find it's easier to reconfigure than the gang valves, plus in the long run it's cheaper. It's a bit more work to set up initially, but much more flexible.
And don't forget a check valve!