Well I re-used the old springs, since the Koni FSD's were OEM - meaning they had the same height/size. The only time you need to replace springs is if they are bad/damaged or if you want to lower the car.
You are absolutely correct about the rear being a pain. Simply loosing bolts and taking it down didn't give enough clearance to take the springs/struts out.
The way I did it, was get a 2nd person to help me out. While I used a huge pry bar and pushed down on the rear axle, the 2nd person started wiggling and jiggling the struts out. I'm not sure if that is how it's supposed to be done (probably not) but it worked without damaging anything or taking more stuff apart.

 

I really appreciate your quick response. I think I will use the existing springs.
This is the Koni kit that I am planning to purchase. Any complains on your Koni yet?

Audi B6 A4 Quattro V6 30v > Suspension > Shocks > ES#263013 FSD Shocks & Struts Kit - 2100-4002

Thank you!

 

I bought the same Koni's except for the V8 model (since I drive the 4.2). They are great and I still love them.
The only regret I have are the control arms - I have to replace them again. What a waste of money.