The oscillators on the Supernovas are more flexible than they appear; even though it only have saw and square/pulse waveforms, it has the "hardness" (Or was it softness?) parameter that is like an individual low pass filter for each oscillator, and each oscillator also have it's own slave oscillator for sync.
That is from memory from research when I was considering getting one, so someone please correct me if I'm wrong.
The supernovas are 16-part multitimbral whilst the KS just have 4 parts if that matters to you.
As for the vocoder, dunno about the differences, but I love this KS demo: