Quoting DJ.: 4 any other option I'm not aware of
I've discussed this with a friend and he thinks the big advantage of supercharging a standard engine, is if it goes bang, you can just source another relatively cheap engine and move the charger over to that.
It may be different for the Sigma, but normally if you're going to do forced induction properly you need to reduce the compression ratio and maybe beef up the crank. Which means if it goes bang, you can source another cheap engine, but you'll need to lower its compression ratio before bolting on the supercharger again.