Sport jacket is all men need to respect the dress code.
On the few nights when a tie is required in Atlantide, you can opt to dine in Hot Rocks or La Terrazza or the pizza place or opt for room service. It really is not an issue.
I'm not sure why some passengers even care. I surely do not care what any other passenger is wearing provided that the attire is respectable. Silversea gives you options. Use them
In fact, Cunard gives you options too. You can avoid formal attire but it's not as much fun as puttin' on the Ritz IMO