I think it might be a good idea to summarize everything that we now seem to know about this situation.
The DTS identification on your AVR does not appear to be a bug. Also, this "issue" seems to be unrelated to the "low volume" issue that is reported by some users.
Regarding the "DTS" issue:
For the sake of simplicity, I will only address "advanced" mode authoring, as this is what the US discs apparently will almost exclusively be released in - so forget about "standard" mode for this discussion.
The A1/XA1 units will decode DD+ on the HD DVD discs to PCM internally, where the audio is mixed with special features (such as button presses, messages, audio-visual commentary, etc).
This PCM (typically 96/24 5.1 audio) is then output to the DACS (digital to analog converters) in the player and output to the analog plugs (using this 96/24 5.1 PCM stream).
This PCM 96/24 5.1 stream can also be sent directly into an AVR via HDMI so that your AVR can use it's own DACS instead.
The analog plugs on the A1/XA1, and the HDMI/PCM transfer are the two best (i.e. highest quality) audio outputs you will get from these players. No reconversion of any sort will happen when running in these modes.
HOWEVER - for many users who use SPDIF (ie TOSlink optical, or coax) there needs to be this option also for getting the audio into their AVRs.
Because SPDIF cannot get anywhere near the bandwidth required for 5.1 96/24 full-stream audio, Toshiba has implemented a clever, and very elegant solution. It takes this 5.1 96/24 PCM stream and converts it in real-time to DTS audio and sends it over SPDIF to your AVR, for decoding.
We are assuming that they chose DTS over DD because DTS allows up to 1.5 megabits per second and would be considered the best option over SPDIF bandwidth. There are likely a few people who would disagree and state that DD (Dolby Digital) at 640 kilobits would be better. But I personally think Toshiba made the right choice here. If you choose to do PCM over SPDIF, you will get a two-channel (2.0) 96/24 stream instead.
So you have three choices for how to get the audio out of the A1/XA1. The way I view it is:
1) PCM over HDMI - Best (5.1 96/24)
2) Analog - Next Best (5.1 96/24 converted to analog)
3) SPDIF - Third Best (5.1 DTS)
I do not believe at this point that this system has caused any of the problems being reported with audio quality.
Also, while a couple of users reported hum from the analog ports, this turned out to be "ground feedback" caused other equipment that was connected in their setup, which they were able to isolate and correct.
Intriguingly, some users have reported observing 6.1 audio being sent to their AVR over this DTS link (I think from the Universal disc). I've seen a note somewhere that seems to confirm that this DTS real-time encoding *does* preserve the matrix information required for this, but I'll leave that one for Toshiba or DTS to confirm here.
EDIT: If so, you will also get this 6.1 matrix data over PCM also.
EDIT: I believe I recall that one analog user reported seeing a message indicating this in the thread, but I'm not certain how this would work with analog.
NOW - THE VOLUME ISSUE:
Users have reported that on Warner titles, the audio level is much lower than the audio from their other devices, or from regular DVDs in the same Toshiba players.
Interestingly, they have reported the audio to be at the same weak level (8 to 10 db below normal) whether they choose to use Analog, HDMI or SPDIF connections. This immediately rules out the DTS re-encoder as the cause - IMO.
Also, they report that the audio level is perfectly normal with releases from Universal - again, on all output ports. To me, this rules out the internal mixers in the Toshibas, and points the finger at the audio encoding on the Warner discs.
I believe that someone goofed when encoding the audio for the Warner titles that have exhibited the problem. We will have to wait for some industrious soul to confirm this with measurements, but I'm pretty sure that this is the case.
It is easy to see how someone may have seen all these new learning experiences all run together as a blur and link one to another as a bug, but it appears to be all OK - except for the Warner discs, of course.
Yes, it would have been useful to know before-hand what to expect when connecting the A1 to an AVR via SPDIF, to avoid all the confusion - but at least we understand now.
Yes - the A1 player will be decoding the full 5.1 DD+ and doing it's mixing, etc, then outputting DTS to your AVR over SPDIF. So you might think your AVR is decoding 5.1 DTS (and it is) but your player is still decoding the full 5.1 DD+ from the disc.
And you'll still get the full 96/24 5.1 PCM audio decoded from the DD+ stream, over analog and via PCM/HDMI.
This DTS issue is not a bug, and the audio does not seem to be adversely affected by the re-encoding at all.
Hope this has helped!