No surround over HDMI

I have an Arris IPC1100P2 connected to a Yamaha YSP 5600. By setting "Audio Output" to "Pass Through" in the "User Setting" menu of the  "BUI MAIN MENU", my YSP 5600 has previously reported receiving "Dolby Digital/Dolby Surround" (5.1) over HDMI from the Arris STB.  However, this is no longer the case. No matter what settings I choose, the YSP 5600 shows PCM stereo (2.0) being received from the Arris over HDMI.

Interestingly, if I connect the Arris to the YSP 5600 over optical cable, the YSP-5600 again shows "Dolby Digital/Dolby Surround" (5.1).

Does anyone have an idea what has changed, or how I can recover 5.1 sound?

My Arris IPC 1100p2 shows software release APR-4.8 and Build number: 16.15

Re: No surround over HDMI

I had no surround over HDMI, optical, or coxial. Went to the dashboard (the green D key will get you there), TV support, select set top box, run the auto correct.

It downloaded firmware again, and when it was done (just wait for it to say "press Menu") surround was back. Surround over HDMI is fine again.

PS I have the STB going HDMI into my receiver first. Other hookups may have other results.