Nearly all Sony equipment does have discrete On and Off, with function numbers 46 and 47. However, the device numbers can vary. The CDP-CE500 may use device numbers different than sent by the URC setup codes. Are you able to control any functions? If you or someone is able to convert the URC code number to a device number, then we can generate Pronto Hex that "should" work.

Of course, this is the lowest price player Sony sells. It is possible that it is re-branded equipment made by somebody else.