The feature you are looking for is HDMI standby pass through. Don't know if your receiver offers this as it is a Home Theater in a Box system.
After quickly looking thru the manual it doesn't look like your receiver offers this feature.
So your best option is to connect the DirecTV box straight to the TV via HDMI so you can watch TV w/o the receiver on. And also connect an optical cable from the DirecTV box to the receiver for when you want to use the receiver for audio.
HDMI audio and optical audio is the same for a DirecTV box. You'll be able to get Dolby Digital 5.1 with either connection.