As you've noticed, the HD-A2 lacks a 5.1 analog output. This is an issue because the new formats (both HD-DVD and Blu-ray) include three new audio formats: Dolby Digital Plus, Dolby TrueHD, and DTS-HD. TrueHD is a lossless compression format (it uses DVD-Audio's MLP, in fact), and all three are a step up from our old friends Dolby Digital and DTS. They are also too big to fit across an SPDIF cable (coaxial and optical audio cables), meaning that you must either use HDMI v1.1 or higher to carry the digital audio or convert to analog and use the 5.1 analog output.

The Toshiba players do have an interesting trick up their sleeves that many people have reported to be surprisingly good: they can decode Dolby Digital Plus or TrueHD (the players lack support for DTS-HD at this point) and re-encode as high-bitrate DTS 5.1 that can go across an SPDIF (coaxial or optical) connection. If you were to get the HD-A2, that would be the only way you could get these new formats. Since I don't have an HD-DVD player, I can't say just how much difference can be heard between the two approaches. The HD-XA2 that's due around the end of the year should include a 5.1 analog output, if that makes any difference.