Ken, Both scopes in question the 6" Dob and the 4" Mak have 1.25" focusers, I believe, so 2" accessories won't work.
Re cassini div, you don't need to practice squat.
It's obvious to most first timers when conditions are right. It is true that you will see more and more with practice.
Mars is a tough one for newcomers, even when it's relatively close to Earth. I showed Mars to about 15 people a month or so ago through the ED80. Only one could see any surface detail. And he was the only person there who owned a scope.