I tried using the old Marantz CD67 OSE (to downgrade, if the sound was ok) through the onkyo, and I heard a massive difference (the Marantz CD63 KI was much better, as it should be).
I heard that the Sony BDP-S350 blu ray player was pretty good with cd's, so tried it, but it was no way near the CD63 KI.
If your using an old Cambridge Audio DVD player, my guess would be that a 'dedicated' cd player, like the ones you mentioned, with sound superior to it.
Best way to find out is to take your dvd player to a shop, and audition them both in the shop...
Hope that helps.........