Well, we don't know anything for sure, but personally I would expect the 997 to be able to use Pro Logic IIx in conjunction with most any 5.1 source (Dolby Digital, DTS, DD+, TrueHD, DTS-HD HR/MA, or 5.1 PCM). Depending on what they do with DSD bitstreams, that might not be able to work with PLIIx - if it goes DSD straight to the DAC, it would be impossible, but if it went DSD-to-PCM it would be an option.

This ability was rare on early HDMI receivers due to processing requirements, but there are a lot of receivers now that can do it.