That would be correct. Pro Logic II extends two-channel sources to 5.1 and as such is not applicable when working with 5.1 sources. (Pro Logic IIx can be used with 2.0 or 5.1 to create 7.1, but only if you have enough speakers.)

Here's a handy trick that the 970 carried over from the 950 (which I used to own): when the processor first acquires a digital signal, the front panel display lists the specific format of the signal. Common examples are "PCM 48k" (PCM stereo, as found on CD's and some TV channels), "DolbyD 2/0.0" (Dolby Digital 2.0), "DolbyD 3/2.1" (Dolby Digital 5.1, with the "3/2" referring to three front channels - left, right , center - and two surrounds), or "DTS 3/2.1" (DTS 5.1).