In simple terms :

SRP = One application 'All in one'
Step 2 polish = As in name STEP 2 (from a three stage process)

At a minimum the step 2 neads sealing in with a good wax (with no cleaners) i.e. NXT or SRP over step 2 = step 2 completely removed.

and remember that a crap wax on a well preped surface will look far better than a top wax on a badly preped surface.

Although most of my stuff is megs pro range if your applying to the white turbo in your sig and you dont want to throw a full day at it - stick with SRP