AQs is not a premium hand but you are getting 3:1 on a call and closing out action. The short stacks have a big range. The big stack just flatting is odd. Either they have a monster and want a call or are just taking a chance with a speculative hand on busting out two players. I would just call in that spot hoping to improve on the flop. You are going to hit a 4 flush, A, or Q like 30%. If you don't improve on the flop and V1 bets you can just fold. 20K is a big investment but you have a chance to knock out 2 and more than triple up. By just raising pre you give the big stack a chance to push and put you in a tough spot. If you shove pre you still are still facing two all in and a only a better hand will call. This is a call for me.