It is rather hard to make blanket comparisons between the SD40 and Audya, but I can say the Audya seems to have a slight edge in sounding live, but not that much. If you were ask about other differences, it would be a different story. The Audya is the flagship with added connectivity e.g., 4 sub outs, 2 two mics, and Block Regs(unlimited set lists, organ draw bars, and probably other things.
OTOH
SD40 has new a OS that is faster and more direct than my Audya, and newer features and beautiful touch screen. I really like the SD40, at 4 lbs, for all my singing and playing needs. You didn't ask that, but I threw it in.

The comparison of the Pa4X and Ketron is too close to call. I like the styles of both equally, but differently. Both are top notch, and the rest subjective. As far as sounding live, Ketron might have a slight edge to us, but the audience will notice the structure of the style, not the DSP difference. They are both great, live sounding machines.

That's the best I can do my friend.