Sulfite also drags the oxidation of HQ to the right by scavenging the quinone by generating HQ monosulfonate which itself is a weak developer.
But, as a number of people have said, the use of more than two developing agents is a real reach. I know that Haist has said that, and probably Henn and Lee as well.
BTW, I have also made mention elsewhere of ETA developers. They are distinguished from superadditive developer combinations by having the pH adjusted to be optimum for the primary developer. The primary developer is present at very low concentrations. The other developer is not really active under these conditions except to regenerate the primary developer. These are unique and AFAIK there are not currently on the market.