6.4 will work fine. The 21.0 would be even better since it can learn. Both are cheap and plentiful on ebay. If you're not married to a Dish remote or need RF, many universals would be better since they are cheaper, learning, control more devices, assign any function from any device to any key and can do macros ("activities"). The $15 RCA RCRP05B is such a remote and available most anywhere.
