DVD-A is one of the two types of high resolution music (SACD being the other). With a DVD-A, you not only get the hi-res audio, you usually get a DTS (or a Dolby Digital) 5.1 layer as well. Not to mention a regular PCM 2.0 layer. If you have a player that can play DVD-A and a receiver that has the 6 analog inputs, then you can listen to the hi-res portion of the disc. If you have a regular DVD player, then you can listen to the DTS/DD layer. If you don't a 5.1 speaker setup, you can listen to the DTS/DD layer downmixed to 2.0, or you can listen to the 2.0 that is usually provided.
Another nice thing about DVD-A is that the discs usually include video stuff too: promo videos, interviews, concert footage, or even printed lyrics. That's something that SACD can't provide, by the way.
If you're listening to the hi-res portion of the disc, then your player is doing the decoding, and sending that to the receiver through the analog cables, where the receiver simply routes the information to the appropriate speakers.
Apparently, DVD-A can be ripped, but you need a lot of software to do it. You can possibly download it, but they would be monstrously large files. It really doesn't even seem worth it, but if you can find a site, you'll see how big those files are.
Hope I've helped!
cheers,
supervij