a technics or midi file is only a control sequence requiring your piano or a pc soundcard for playback. To make an mp3 you must play the total performance (from sequencer say) from the audio line out of the piano into the line in of your pc soundcard into a wave recording program, then saving as mp3. Alternatively, and much superior, is to use the usb connection to the Audio Recorder on the supplied CD or other wave application. Mp3s from Audio Recorder are highly compressed but if you get that far there are plenty of free programs to provide mp3s of whatever quality level you require.

Midi is the only format suitable for direct play since a streaming 16 channel data flow. Technics format is many other things apart from sequence information and has to be loaded into piano ram to provide banks of patterns, pads, sounds, registrations, effects etc. You could make a multitrack technics song sequence, save it as midi and play it direct if you so wished, then you would just have a song.