Dolby 7.1 is the exact same thing as Dolby 5.1, except that 7.1 has two
additional channels that are derived using a process similar to Dolby Pro
Logic. In other words, the additional two channels are not two discrete,
separate channels, but rather are derived "effects" channels. 

5.1 is the maximum number of discrete, separate channels available in a
consumer-level delivery format. So the passthrough is for both 5.1 and 7.1. 

The Micro/Amigo/SRM S/PDIF Out can pass both Dolby Digital and dts encoded
data streams.
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