Reading this <a href="http://www.dolby.com/consumer/technology/trueHD/AVRs/trueHD_avrs_2.html">page</a> on Dolby's website I was wondering if current AVReceivers are actually interpreting a high bit-rate Dolby Digital stream as DTS?
S/PDIF Connection
If your A/V receiver or processor has neither multichannel analog or digital inputs, but is equipped with 5.1-channel Dolby® Digital decoding and playback, you will still be able to enjoy 5.1-channel performance from next-generation optical players. Included within 7.1-channel multichannel Dolby Digital Plus and Dolby TrueHD streams is a core 5.1 mix prepared by the content maker that is used when the player is set for 5.1-channel mode. After playback audio signals have been mixed in the player, the PCM signal can be encoded to a Dolby Digital signal and output from the player via S/PDIF (optical or coaxial) to your connected Dolby Digital A/V receiver or processor.
In many instances, the audio quality you will experience from this connection may be better than what you would experience during playback of standard-definition DVD-Video discs, especially if the native signal on the disc is Dolby TrueHD or high-bit-rate Dolby Digital Plus. This is a direct result of a higher-quality source signal feeding a Dolby Digital encoder running at 640 kbps—higher than the maximum bit rate on DVD-Video.
It sounds as though a 5.1 Dolby Digtal stream derived from the DDP or Dolby TruHD source is encoded at 640kbps by the player (448 is highest on SD discs) and then output to the amp. 640kbps is fairly close to half bit-rate DTS at 768kbps.
Just a thought really. It sounds as though if the Tosh HD-A1 offered multi-channel outputs you'd get the full benefit of HD audio.
EDIT: Alternatively, the review on <a href="http://www.dvdtown.com/article/reviewofthetoshibahd-a1hd-dvdp/3255/">DVDTown</a> for the HD-A1 says Toshiba went with a DTS encoder instead of the Dolby option for their first players.