I love my P4SS .I have spoken to Williams re the Suplex kit and they tell me the set up on the SS is very good and Suplex would not be required.
I find it so much better than my standard Plus 4 that I have decided to leave it alone as advised.
The down side of the P4SS is that it sounds so good when thrashed you can't help giving it a boot full at every opportunity.Hence my first Mog speeding ticket!!