I'm wondering if this is going to solve the issue people have with older home theater receivers that can't decode DD+. Dolby itself says that DD+ when output over S/PDIF (optical, in this case) is down-converted to standard DD 5.1.
Excerpt from DD+ page:
Is Dolby Digital Plus content backward-compatible?
Because Dolby Digital Plus is built on core Dolby Digital technologies, content that is encoded with Dolby Digital Plus is fully compatible with the millions of existing home theaters and playback systems worldwide equipped for Dolby Digital playback.
Dolby Digital Plus soundtracks are easily converted to a 640 kbps Dolby Digital signal without decoding and reencoding, for output via S/PDIF.
The 640 kbps bit rate, which is higher than the standard 448 kbps used on DVDs, is fully compatible with all existing Dolby Digital decoding products such as A/V receivers, and can provide higher-than-DVD quality from Dolby Digital Plus soundtracks when played back through existing systems.