fred roller:
I make gross assumptions that audio dvd means you just put audio formatted files on a DVD of course, so please take with a grain of salt.
DVD-audio (or DVD-A) is a different beast than DVD-video (the names should give you a clue about purpose), and vastly different than random kinds of audio data files that happen to be on a DVD (but could be on any medium).
DVD-audio was intended as an usurper to compact disc digital audio (large disc capacity, room for lots of audio, quality-wise, time-wise, and/or multi-channel). But it never really took off and DVD-audio is a rarity, and finding a player for it is even more unusual than finding the discs. I've never seen any in a shop, I think it'd all have to be special order.
A DVD-audio disc is not going to be played by most DVD players, only ones that deliberately support it will do so. Of course you can encode a selection of audio tracks to a DVD-video, and get a few hours of playback, that way. But the quality will be inferior due to the compression. Though, if you want a disc that can play for a couple of hours, or more, that may be more convenient than a compact disc.
And for something that you can playback in a car, you definitely want to make it start playing the files immediately, and progress through them all, so you don't need to navigate menus just to begin playback (unlike most movies).