From the dispay of the 970 how can you tell if the Dolby Digital EX encoded source contains the extra back channel? I think the 970 will display 3/2.1 for both DD 5.1 and DD EX sources because the extra back channel is matrix and not discrete. The reason I ask is that DD EX is avialible from the surround modes on all DD 5.1 sources. Is there anything that indicates if the soundtrack contains the extra back channel?

Dolby EX material's bitstream is identical to regular Dolby 5.1, so the 970 will display 3/2.1 for both. There is a flag that many EX tracks use to force the receiver or processor to apply EX decoding (the Lord of the Rings EE discs include this flag, among many others. Other discs (such as the Star Wars discs) include the matrix encoding for the surround back channel, but the only identification is the packaging.

I generally apply Pro Logic IIx decoding to all Dolby 5.1 sources (unless the EX flag is present, in which case the flag forces EX decoding whether I like it or not), and since PLIIx is a matrix decoding process it works just as well as EX would with those unflagged EX tracks.