Just found this post on the Directv technical forums by litzdog911.
Two things need to happen before your HR20 will see this new subchannel ....
The station must provide their new subchannel information to Tribune News Services. That's where DirecTV gets their channel database and Guide Data. Check Tribune's site at
http://www.zap2it.com to see if the station is listed there.
Once the subchannel is added to Tribune's database, DirecTV must add that information to the database and Guide Data used by the DVR/Receivers. Unfortunately DirecTV is getting much more restrictive here, supposedly due to database capacity and performance issues with so many new subchannels around the country. Be sure to email DirecTV directly and keep your fingers crossed.