What are you using when machine polishing?

On your car I'd recommend Menzerna PO106 Final Finish on a Meguiars polishing pad (then maybe the same polish again on a finishing pad depending on how well you've worked it and refined the finish).

Failing that step up to Menzerna PO85 RD 3.02 Intensive polish if the above doesn't work followed by Menzerna PO85 Final Finish to refine.

All depends on what you're trying to do - just get a deeper more reflective gloss on the paint or a full correction and swirl removal. If it's the former then go with the first set up I suggested, and for a full correction go with the Intensive polish > Final finish. As with all machine polishing, always start with the least abrasive pad/polish combo you've got and work up, which I'm sure you already know.

You can get a Menzerna 250ml starter kit from a lot of detailing traders and it contains 4 bottles (the 3 I've mentioned above plus a heavier cutting compound called Power Gloss, but you won't need that).

As for a good wax or sealant that works well on silver, try either Collinite 476s, the Jeffs workstat Acrylic Jett, or one of the Dodo range like Diamond White or Light fantastic depending on whether you want a hard or soft wax. Another new paste sealant that's getting great reviews at the moment is Finish Kare's 1000p, although I've yet to try it myself, I have it on good authority that it looks great on silver and is extremely durable (even a match for the Collinite in this respect). Zaino is another route to go down that always produces great results on light metallics.

Silver is a difficult colour to get a good depth of shine and reflections to, but with the right knowhow and products it's achievable.

Hope some of that's helped, mate