This explains it in detail. I don't recall seing this in the maual, I'll read it again. I was thinking that the optical output did not fully support multi channel sound per reading other posts. Thanks Alex!
Question: When using a digital audio input, I sometimes see the message "DS - OFF" on my AVR receiver. What does it mean?
Answer: The "DS - OFF" message will appear in conjunction with "2.0.0", which is an indication of the channel configuration of the incoming bitstream. You may have realized that this means data is present for the front left and right channels only. "DS" stands for "Dolby Surround", and the message means that the program is not encoded with Dolbyµ Surround, that is, Dolby Pro Logicµ information. Therefore, the AVR recognizes the stream as a Dolby Digital 2.0 program.
However, you may enjoy surround sound with this type of program by manually activating Pro Logic processing. Using the remote, press the Dolby button repeatedly until the desired Pro Logic mode appears in the display, or press the OSD button and use the navigation keys to access the Surround Select and Dolby menus. Using the front-panel controls, make sure the Dolby group has been selected by repeatedly pressing the Surround Mode Group Selector button on the left side of the button group until the Dolby group has been selected. Then repeatedly press the Surround Mode Selector immediately to the right until the desired Pro Logic mode has been selected.
The "EX - OFF" message will appear with a "3.2.1" channel configuration. It reflects that the Dolby Digital bitstream is not encoded with information for the surround back channel which is used in Dolby Digital EX materials.
Again, if your receiver has been configured for 6.1 or 7.1 operation, you may enjoy EX processing by manually selecting the Dolby Digital EX mode using the procedure described above.