Never mind the above post - got the answer off Wikipedia. I was also surprised by how few DVD-audio and SACD titles are available at Amazon.
On another topic, I hooked up a Blu-Ray player to my 2.0 stereo, and it really seems it wants a video screen to adjust its' settings, (such as picking the audio format). One can certainly see why the manufacturer expected it to be used with a video screen, but are there models which don't make this assumption and are intended for audio-only systems? Or do I need to attach a small monitor to it just for use in navigating menus?