[GregY]

Does DVD-A play at top output on all DVD players, or only ones compatible with DVD-A? My best understanding is that they play in standard DVD players, but not at top quality - correct?

Most commercial DVDs will contain a Dolby Digital track that will play on all DVD players. The high res (either stereo or multichannel) layer(s) will only play on a player that can do DVD-A.

Where do 24-bit FLAC files fit in with that?

You can burn a DVD-Audio disc with 24-bit files or you can just burn an audio only regular DVD without converting. That is, you don't have to burn to DVD-A. Regular DVD supports up to (I think) 24-bit 192kHz.

what about Dual Discs?

Nothing more than a CD and a DVD (or DVD-A) glued together. Don't play in some players as they're a little thicker than normal CDs/DVDs. Many DualDiscs don't even have high res tracks - they're being marketed more for the video content than the high res audio.

You can get into SACD and DVD-A without spending alot if you already have a good 2-channel setup. The Pioneer 563A plays both DVD-A and SACD and is a great entry level player.

to those who have upgraded, has the amount of DVD-A/SACDs released by the labels, plus the higher bit rate boots, been worth the cost?

I really like SACD. I don't listen to alot of multichannel, basically just stereo, and I don't have a great setup. But I think SACD is worth it, especially if all it requires is a combo player purchase like the 563A.