Today I received the HR24-200 that I bought for 15 bucks on eBay. Upon inspection of the inside, as well as the inside of my HR21PRO-200, it became rather apparent rather quickly that my "grand plan" was nothing more than wishful thinking. The plain and simple fact is that the main boards are way too different for there to be any hope of installing the HR24 main board inside the HR21PRO. The boards are different sizes and mounting holes are in completely different locations. As another example, the access card slot is integral in the HR24, but resides on a separate, small board connected to the main board with one of those short, flat multi-conductor jumpers. There's just no way to adapt one to the other without having the entire Samsung factory at your disposal. Every single connector to other items, such as front panel USB port, rear panel connectors, all different. I suppose it's not impossible, but way above my pay grade, which is pretty high! I think at this point my only hope is that some day DirecTV will once again release a "pro-grade" rack-mount DVR, whatever model it may be.