For me the addition of a CDR into a keyboard means just another piece of mechanical kit that probably won't last for the life of the keyboard & when it breaks down it will create all kinds of problems.
I would far rather see the money spent on what for me is the most paramount importance the quality of the voice samples so my most simple requirement would be an easy & reliable two way connection from keyboard to PC so that if I need to record I can get the best quality sound production to either minidisk or pc & talking of the minidisk
I was always under the impression that the Sony marketing strategy was to make it the world leader as the main music storage medium
Johnnie