I can confirm that the Pioneer DV563A does in fact play MP3 files from a DVD-R. I burned approximately 3.5GB of MP3 files onto a 1X DVD-R this afternoon (Nero v6, ISO, single session, relaxed everything) and put it in the player just a few minutes ago. The display shortly showed "MP3", and when I hit Play, it started playing. I had the digital (optical) output selected, so the analog outputs aren't necessary for MP3 (why would they be?

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The on-screen navigation menu shows the full directory and file names, and allows me to move throughout the hierarchy with ease. I was happy before, but this is great!
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- Jeff