I know them Akais. They have a first-class tape transport and fine sound heads but sometimes lazy electronics, that is that the record amplifier clips still before tape saturation is reached in the trebles.
Does your Akai have a built-in mixer? Else, you can mix in the air. It is astonishing how good four generations of air mixing using simple speakers and microphones can sound.
Sound-on-sound needs two tracks. One track is played back, and the sum of this signal and the signal that you play live to it is recorded on the second track.
Do you have a compact casette tape deck? You can record the first track, mostly the rythm, to the CC deck, and then do two times SOS on the Akai, and then go back to the CC. Now you have recorded four generations and have all of them still available.