Mandatroy and optional Surround codecs for HD DVD players.

DTS 5.1 - Not included.

DTS HD - Mandatory (DTS core only, compatible with
standard DTS decoders on market today).

DTS HD Master - Optional (up to 192khz/24 bits).

Dolby Digital 5.1 - Not included.

Dolby Digital Plus - Mandatory.

Dolby Ture HD - Mandatory (2 channels only).
2 to 7 ch.

5.1 channel PCM - Not included (192khz/24 bits).

7.1 channel PCM - Not included (96khz/24bits).

All surround formats passed through a SPDIF will be transcode to DTS 5.1. Optical has a bandwidth of only 1.5Mbps and therfore can not pass the higher transfer rates of Dolby Digital Plus or DTS HD. Both of these formats are limited to 3Mbps with the current form of HD dvd's regardless of how many channels are on the disc. Producers could expand on that by at least 2Mbps in later version of the disc if they so choose.
Just for the record the Toshiba HD-A1 will output hi-def over both HDMI and component outputs. However, HD DVD producers may include copy protection instuctions in their discs that prohibit output over the component out jacks. In this case you will have no choice but to utilize the HDMI output.