Sorry - I should have put this in my original append...
DVD-Audio discs, along with SACDs, are positioned as the possible successor to CDs. While DVD-Video discs play both video and audio, a DVD-Audio disc is primarily for audio with video as a backdrop.
The DVD-Audio disc uses the same menu system as a DVD-Video disc. The big difference is that DVD-Audio discs can have up to 192kHz, 24-bit PCM sound. For 5.1-channel output, the maximum sampling rate is 96kHz, 24-bit sound and is encoded with MLP lossless compression. Standard CDs, on the other hand, use 44.1kHz, 16-bit two-channel sampling. So, the DVD-Audio disc sounds better than a CD and with more channels. I notice the lower-to-mid bass and the upper treble (such as cymbal ringing) as the areas with the most improvement.
Each DVD-Audio disc also contains a DVD-Video layer for compatibility with DVD-Video players. This layer always contains a 5.1-channel Dolby Digital track and sometimes also has a DTS 5.1-channel track. It is the Dolby Digital track that I believe the XLR's system is playing.
Hope that helps explain DVD-Audio. Glad no-one asked about how an SACD is formatted (I couldn't tie that to an XLR anyway except to say that the CD layer of an SACD will play in the XLR)!