I have a couple of DVD Audio discs. By this I mean discs that are DVD Audio spec, not DVD-Video discs that contain music videos or whatever.
This format may slowly increase in popularity because they are now releasing two sided "universal" discs that have Redbook CD Audio on one side and DVD Audio on the other side. Dont like flippers but shrug
Most / all DVD-ROMs should support DVD-A if you have a software player that supports it such as WinDVD 6 with the DVD-Audio pack or whatever they call it. There is no known crack for DVD-Audio encryption which makes it unrippable UNLESS the disc is not encrypted (I think.) You should have a card that's capable of true 24/192 on all 6 or 8 channels, such as some of the M-Audio cards. The Audigy 2 is not capable of this, not sure about the A2 ZS the 24 bit Live! or the "Audigy 4". Many DVD-As are only 24/96. It is suspected that WinDVD downsamples the audio which worsens the sound quality (at least theoretically.) Currently, DVD-Audio players sound better in almost all cases, compared to audio out from a sound card and dvd-rom.
Audio formats can be upto 192khz / 24 bit. Data can be either PCM either completely uncompressed or lossless compressed using a process called MLP (Meridian Lossless Packing), DTS or AC3. Stereo or multichannel. The format has an optional flag that will force players to block even 2 channel PCM digital out, leaving only analog output. The "expected" output of a dvd audio player is 6 channel analog, but there is some movement towards digital DVD-A output. The "old" digital connections cannot support multi-channel DVD-A output because of the bandwidth requirements, but could support 2 channel output at maximum quality. Many standalone dvd players will not output digital audio at all sent to a receiver / multi-channel preamp or HT processor the way DVD-Video's sound is.
In an ideal DVD-Audio setup, all 6 speakers are full range identical speakers. i.e. it is not necessary that the 6th channel be "LFE" / Subwoofer / Sub-bass only. This is actually used on some audiophile discs.
In reality, at least 5 channels should be identical speakers, and of good quality, not a $100-$300 "5.1" computer speaker set. As things stand now, this is for audiophiles with lots of money to spend on audio. It will work with a basic computer and 5.1 cheapo speakers, but may not sound any better than the average Dolby Digital 48khz/16 bit highly compressed audio track because the resolution is just not there in such a setup.
One of the drawbacks of this format is that you usually cant pass the data digitally to your receiver as you can with AC3 from DVD-Video. Some receivers now support lossless over firewire (usually called i.Link), such as Pioneer with their Elite line of receivers and players. Don't know if this is a standard but more than one company is doing it. Denon went with some proprietary ethernet based standard for lossless digital to their receiver.
It is meant to be playable without a video screen (i.e. menus optional) just like a CD. Some older discs are less friendly in this regard.
Sound quality with GOOD speakers (> $1000/pair) and a good pre-amp and a good player (all costing a minimum of > $1000 each) is noticeably better than redbook in many cases, but sometimes not even then (depends on the player and source.)
There are some really good redbook players in the > $1000 range that can compete with 2 channel DVD Audio or SACD sound, such as the Meridian G06, but these are not aimed at the mass market, and this is while DVD Audio is still a new format. Eventually DVD Audio will clearly outstrip CD Audio in quality. Remember how crappy early CDs were from the early 80s? People didnt have the equipment, experience, or processing to produce quality CDs. Even current popular music CDs are not that well produced compared to audiophile labels such as Telarc, etc.
What's strange is while one end of the market is focused on better than CD quality audio (SACD/DVD-A) the other end is all caught up in worse than CD Audio (MP3s/WMA/OGG) in the name of saved space. Once drives get small and cheap enough, people will be recollecting their mp3 collection in lossless or high-res audio, maybe.
Hope that helped.