Drive replacement is difficult but possible. You have to use specific drives of the exact models that are loaded into the firmware, or they will not marry and will not work with the receiver. Drives that work in models 501, 508, and 510 can be placed in any one of them. So you can go up to whatever the size was in the 510. The problem is getting the drive married to your particular receiver. Recommend the Yahoo group dishmod for this, which includes files and procedures and disk drive model numbers that will work.