You are correct about the polyphony. They are both 48 note however the difference in the "live" piano and the piano in the 300 is enough for those looking for a good piano sound to look at this model especially now that the price is $299. Also, this arranger allows the player to turn off any of the style tracks they would like to mute just like the higher arranger models. The 300 is either only drums or everything else is on. With the 400 I can have Drums and bass, or just bass or any one of the other style tracks only or any combination of them all.