My mom has a legend. On hers you have to disarm the alarm/killswitch before it will even crank. Is there an alarm or something you have to disarm? It sounds bizarre that it won't even crank since the battery and starter appear to be fine. The last thing to check would be the starter circuitry itself. Maybe something came loose.
I agree about the beastness of the Legend. I love driving my mom's. The ride is so smooth and the power is just waiting to be unleashed. I hope you find the problem because it is a great car.