Suddenly, as of a few days ago, I am unable to get Dolby Digital audio from my Scientific Atlanta cable box.

There are two hook-ups as follows:

1)cable box to TV: HDMI
2)cable box to Pre/Pro: optical

One of two settings used at any given time with cable box:

1) Audio Out = HDMI
2) Audio Out = Dolby Digital

It is with setting #2 (Audio Out = Dolby Digital) that I no longer get any sound. None of the speaker icons on my pre/pro light up whereas before they did when working properly.

When "Audio Out" is set to HDMI I do get sound but it is PLIIx and not DD.

My Pre/Pro is a Boston Acoustic AVP7 which is a clone of the Sherwood Newcastle P-965.

Any ideas why this suddenly stopped working?