I think the best way to pass is before the X-guard is fully established. Once the X-guard is properly sunk, it is very difficult to escape. It is impossible to establish a good base since the X-guard attacks the base at all times.
I would not worry so much about the foot that is hooked. I would worry more about the foot that is trapped between the shoulder and the neck. If you can prevent your opponent from securing this foot, you can easily negate his X-guard. It should be easy to establish a base and begin a standard open guard pass.
I am no authority on X-guard, but I have always felt as if the trapped foot was a more important part than the hooked foot. On that basis, I would try to free the trapped foot first.