You're stuck with the equipment that you requested at signup for 1 year. And you can only have 1 leased 522 per account. After the year you can pay to be able to lease 1 510 under Dish 'n it up.
You can do a 522/510/510 or a 942/522. However, these are only available at signup. you can do a DishNItUp after either 6 or 12 months(I think it is 12) to get a second 522 if you qualify.