Cambridge Audio 640c V2, 650c, or 740c differences

I want to add a CD player to my basic system utilizing the Cambridge Audio 640a V2 integrated amp.

There must be someone with experience with the Cambridge Audio 640c V2, 650c, and 740c CD players.
... What will I loose by buying the 640c V2 for cheap?
... Or more importantly what will I gain by moving up the line to the new 650c or older 740c
... Or should I just add the DACMagic to my universal DVD player?