Bitt's post is quite helpful, I think. After seeing those images and reading the referenced web page, I am quite certain that my CD player is mounted "DIN-I" style. Only two bolts are used on each side, and the trim ring as well as the sleeve is not used.

I have actually had two different units there, and so would expect a wide range of CD players to be DIN-I mountable. The first was a 50x4 Aiwa - I can't remember which model. But now I have a Kenwood: KDC-X659.