It depends which output board you've got, the Akai one or the MUTEC one*, as to whether the MPC's digital out is a phono or standard jack. As the DAT machine, CD burner & digital mixer I was using all had phono connections I went for the Akai board. It is easier to find proper digital cable with phono to phono rather than phono to jack. An ordinary audio cable might work but it is better to get a proper digital one.
*There were some recent posts about the difference between these two boards.