First gen Minidisc players MZ-1 and MZ-2P have optical outs. Unfortunately they are not very portable and most of their Ni-Cd batteries are dead by now (and only provided 60 min or so running time even when new!
) But I think they do deserve to be on the list.
Another thing I'd like to add if you feel this is relevant, is a column indicating lossy playback yes/no. I'm pretty sure none of the Sonys will output digital when playing MP3/ATRAC CD's. Unfortunately I found that out AFTER I ran out and snatched a DNE20 on eBay but... well that's my bad for not researching. It says so right in the manual. Can the iRiver CDP's run digital out with MP3 CD's?