Have 4 HD receivers - want external DVR - DirecTV

I upgraded my old original receivers to 4 HD receivers. Signal comes in beautifully clear on my new tv's. Now I want to add an external DVR to one HD receiver. DirectTV doesn't have this - only an internal DVR receiver. Does anybody know of an external third party unit that would connect to the receiver, probably with HDMI?

This question, "Have 4 HD receivers - want external DVR," is about DirecTV channels, programming, equipment, and sports.