I have *not* used the PB's/SSR polishes, but I have rather extensive experience with silver Audis. The clear on them is quite hard, so if you have any significant marring I'd go straight to the 2.5.
As a "for instance", I had some *very* light marring on the trunklid of my S8 from where I touched it with a soft piece of cotton (as I said, *very* minor, most people could never see it). I fooled around seeing if mild products would fix it. Nope, I had to go to my 3M PI-III RC (similar, I believe, to your SSR 2.5) and then follow up with a milder product. Biggest trick was actually just *seeing* the problem, it was totally invisible under fluorescents and pretty much so under halogens. Incandescents made it jump right out at me. I used three grades of polish, all on speed six, and a lot of time, to remove this virtually invisible scratch. Hard clearcoat.
Check your work in different lighting conditions. I find high-wattage incandescents to be the best for spotting minor marring especially on silver. An old-fashioned trouble light with a strong bulb can be better than a fancy halogen! Move the light around and move yourself around too, so you hit everything from different illumination/viewing angles.
And don't worry, there's *no* need to be paranoid, or even really cautious, about using sensible products by PC on an Audi. You're not dealing with a fragile paintjob

This is assuming factory paint. But even the repainted parts of ours (done with Spies Hecker paint) are tough.