Early DirecTV receivers had serial ports which allowed TiVo, ReplayTV, and other DVRs to control them without using IR blasters. Serial provides a more reliable control connection as there is no chance of interference or having the IR emitters moved while cleaning, etc. And it offers a bidirectional communication channel so the DVR can confirm the change. But later model DirecTV receivers dropped the serial port, forcing users of third party DVRs to use IR blasters.
I just became aware of another solution. Paterson Technologies offers a serial to USB adapter which allows users of TiVo, ReplayTV, ShowStopper, BeyondTV, SageTV, MythTV, and Windows Media Center to control the DirecTV model D11, D12, H20, H21, H32, HR20, and HR21 receivers. It is more than just a simple serial to USB cable, there is some intelligence built in such as the ability to map channels so you can have your DVR, say, tuning channel ’4′ and the satellite receiver actually being tuned to channel 4-1 for OTA ATSC. You can configure it by connecting the adapter to a PC.
It isn’t a cheap option at $42, but for those using 3rd party DVRs with newer DirecTV receivers it may be worth it for the reliability of serial over IR, and the channel mapping abilities. You can check it out for yourself.