I think the first thing to consider is what model do you have. J, HD, or an SE? The J model would likely not do that well with a 4 way. The HD would do ok, and the SE would likely do fairly well, which brings me to my other point....
What type of wood are you splitting and how long do you process it to?
If its straight grained stuff that's only 12"-16" long and 8-"12" diameter, then I think a 4 way could work. Anything with knots, large in diameter, or longer in length may be too much to ask.
Personally, I feel the Supersplit is fast enough, why complicate it with a 4 way that could make it more dangerous, produce odd size splits, and is prone to damaging the machine. With a single wedge, one person can do up to about a cord an hour if the wood is already in rounds. How much faster do you really need to go?