Typically, if you're running higher pressure in the rear vs. the front in a FWD car, it's to try to get the rear end to "rotate". Obviously, your newfound stiffness has improved that situation. So, a good starting point might be to set your rear pressures the same as the front. or even a few psi less. Find out what it takes to get the rear to stick again, then you can raise the pressures back up from there to get just the amount of "looseness" that you desire.

Alignment = caster, camber and toe. Some or all of these may be adjustable on your car, I don't know. To settle the rear, you want to try to get more negative camber in the rear or a slight amount of toe-in.

Conversely, you could lessen the grip at the front of the car to acheive balance. (I don't like that idea, myself, but if it's the only option...) In that case you would want a little less negative camber in the front to get the front end to give way before (or at the same time as) the rear.

A lot of experienced FWD autocrossers (where's Muddy? PsuedoX?) actually prefer the car to be set up a little bit "loose". With the balance set that way, you're getting maximum ability to apply power and turn with the front wheels, which is what you need in a FWD car. You just have to learn to deal with the fact that if you do anything silly (like braking or abruptly lifting while entering a turn), the back end of the car can catch up with you VERY quickly.