Well, it's been two weeks since I could control my second HR20 due to the new slingobox pro-hd changing the IR remote control chipset.
The bad news is that there is still no driver, including from the guys that made the original S1378 substitute file.
The good news is that DirecTV is working on a new feature for the HR2x software, that will actually work as a workaround for us Slingbox users.
The slingbox software supports remote code 00001 & 00002, using the HR21 for the first, and the D10 (remote code 2) for the second. The D10 code uses the same DirecTV remote control, and has all the buttons mapped (despite being listed for a non-dvr box).
If you have a Slingbox Pro-HD, or any slingobx and don't want to download a custom code, you'll eventually be able to do it.
Right now, however, this feature is part of a beta test known as the Cutting Edge program. If you are interested in it, check out this thread / forum at Satelliteguys (you have to be a registered member to view this area - as it is kinda private, hidden from non-members).
http://www.satelliteguys.us/directv-cutting-edge-ce-discussion-forum
After joining / entering this area, read my FYI thread, and then the latest thread about the HR2x receivers (always stickied at the top, but it changes each week). Keep in mind, you are joining a beta software program, there are risks, and no guarantees. But hey, that's how new features get made!
I confirmed an hour ago that after downloading the CE software (only available at limited times), and setting my second receiver to advanced setup - remote code 2, I can control the slingbox pro-hd again!