Best I can find the first consumer sold cd recorder was a sony, about 1990-1991. I believe your Denon dvd 5000 was sold in 1999. Is that about right. I have a old Sony DVP S500D I bought in 1999. It plays cdrs just fine. Still works great my grand kids use it to watch Disney movies. Why some do and some don`t, sorry I can`t answer that. But if yours don`t I don`t think there is any thing you can do.
Beavis is right on one issue. Even today there is some DVD players sold that will not play cdrs. Even some Sony models.