There was recently a flurry of discussion about audio in the Hands On With Japanese Toshiba Player
thread. Attached is a table provided by Amir from Microsoft. It was translated from the Japanese XA1 manual. It should help answer a lot of the questions people have been asking about HDMI audio output. The info probably applies to the A1 as well.
A few notes on the table.
It is still not clear what type of bit stream is passed for DD+ and DTS-HD if the "Bit Stream" option is selected. Is it the full bitstream? Or is it downconverted to standard DD and DTS Core? The latter seems more likely since it would work with current receivers. If it was possible to pass the full bitstream I would expect two Bit Stream options, one for current receivers and one for future receivers that will support the new formats.
The *3 Down Sampling PCM
notation seems to mean down converted to 48 kHz since the 48kHz rows are the highest rates that don't contain *3.
Bottom line seems to be that the best option is to pick PCM output if you have a receiver with an HDMI input that will accept multi-channel PCM. This should provide the highest quality 5.1 sound.
If you don't have such a receiver but have 5.1 channel analog inputs, it's probably best to use the analog outputs which I expect will convert the PCM output streams listed in the table to analog using the built in "Multi-Channel 24-Bit/192kHz audio DACs".
If your receiver doesn't have 5.1 channel analog inputs either, then the Bit Stream mode should at least pass downconverted DD and DTS (which could still be higher bit rates than most DVDs) to your receiver.
Once there are receivers that accept a DD+ or DTS-HD bitstream, that might be the best option for playing back those formats if the player does not downconvert them.