The pins not specifically used by a shield should act as pass through to the next one up. This means the stack can be in any order. An exception may occur where a shield uses the 6-pin ICSP cluster without corresponding males. I think this only means it may have to go on the bottom of the stack, there may be only one of them, but it is pretty hard for this to be a problem.
I doubt that the Ada shield uses SPI exclusively, it may simply need it for an on-board SD card, which you may or may not require, and can use all the other pins as you may require.