^ This is complicated by the fact that the OPPO plays and outputs many more audio formats than your DirecTV box -- which only outputs traditional, lossy, DD 5.1.
Try this, set the OPPO to HDMI Audio Bitstream. Double check that you have HDMI 1 output from the OPPO cabled to the TV, and that HDMI 2 is not cabled.
On Spears & Munsil, go to the Audio Calibration > Channel ID tests and play the traditional, lossy, Dolby Digital DD 5.1 test track. What do you get on the sound bar?
While that is playing, press the Info button on the OPPO remote. The on-screen Info display will show you what audio format is being read off the disc (bottom line, left). Now use Page Up or Page Down to change that display. The Info display will now show you what's going out on the HDMI cables. Check the bottom line left to make sure DD 5.1 is being sent to the TV.
If DD 5.1 is being sent to the TV and you are still only hearing a 2.0 down-mix on the sound-bar, check your settings for the input you are using on the TV for the HDMI cable from the OPPO. It is likely the TV remembers settings "per input". Make sure the audio settings for that input are set to send a Bitstream to the sound bar. (The optical cable can only carry LPCM as Stereo.)
Once you get DD 5.1 working, the complicated stuff starts. We'll get to that in a bit.