Don't forget to register on Mobile One for the Mobile One Rewards. For every 6 qt case, you can get a $5 gift certificate. This also applies if you have your oil changed by dealer/shop.
I have M1 in my LSD and AT in my 94 RX7. I was able to get 2 qts of ATF replaced (not taking out the torque converter) so no difference noticed. I did notice a smoother acceleration with my differential fluid changed. I also noticed easier startup when using synthetic engine oil. I think PS is a sealed and does not require changing unless it's fouled/leaked.