The Empress Deck is the same as the decks below it, in that it is an all cabin deck. While soundproofing is usually good, you need to look at the deck above the Empress, which is the Atlantic Deck and this is where the main showroom and dining rooms are located. In other words you will probably have some or all of the showroom, dining rooms, and galley, located above your cabin.
Carnival tries to put three people in a triple to the maximum extent possible, but they will put you in a quad if there are no more triples available. The cabins are the same size, it's just that one has an extra bunk bed in it.