Nebraska99- While I too always use SG after AIO, it's just possible that the AIO+P21S look simply isn't what you're after. It's hard to say, being as it's such a subjective topic, but *IMO* P21S isn't the "deepest" look out there. It IS quite reflective, but there may be other products that give more perceived depth on silver. *I* think that BFII, PUPP, and Souveran (and maybe 3M showcar paste wax) give more depth than P21S.
Although it's quite "low maintenance", silver is a tricky color when it comes to getting exactly the look *YOU* like (we have five silver vehicles; they all look different). Sometimes it takes a little experimenting with different products before you find what *YOU* are after on your particular silver paint. FWIW, when I had a silver Benz ('88 SEC) I used Autoglym's Super Resin Polish topped with Souveran (summer) or Meg's #16 (winter).