Better Playback for Strings
The quality of the strings playback is bad. It is impossible to hear fast notes, even when the dynamic is FFF, or I change the velocity to 127. Also, the high notes (pretty much above G5) are really painful to hear. This could be fixed if there were recordings of actual instruments for the playback, instead of computer-generated. I tested this by recording one note of my violin on my electric piano, and the sound quality is already better, even though it was just from recording middle C.