TV Repair Questions? Ask a TV Technician
Well, it looks as though you've been going by the right steps. Unfortunately, the problem is that DirecTV can't possibly stay current on all IR codes for all devices. Also, the DirecTV equipment you received may not necessarily be the newest. I know from experience that equipment can sit as long as a year before it is installed. What that means is that the remote you have may not have all of the latest codes in it's database, and even if you try to use codes from the online database, that doesn't mean they have be pre-stored in your remote.
My next step would be to request a new remote from DirecTV to try and get one with more current code sets. Only problem here is that you can't be sure they will send you a brand new one instead of an old unused one they have in stock. Other than that it would be a matter of trying other manufacturer's codes to see if they work with your TV (This is extremely time consuming and not guaranteed to work). Dish Network remotes have a feature where you can simply search for the right code until you hit it...unfortunately, I believe DirecTV STILL does not offer this feature.
Unfortunately, you may be out of luck.