You can instantiate an Elements class instead on directly invoque "first()" on it. Then you will be able to parse the table you wish with the "get(int)" method:
Elements tables = currentServerPage.getElementsByClass("tabella-voli");
Element secondTable = tables.get(1);
Elements tdElements = currentServerPage.getElementsByTag("td");
Then you'll get a list of Elements, containing all the "td" in the second table.