RM2K3 - CAN WE PRESS TWO KEYS AT THE SAME TIME?

Hi.
I'm working on a piano system that uses the keyboard's number keys (0 to 9) to play the notes and I am facing a cruel issue. The database event codes use ten separate Key Inputs that each check a variable's value (corresponding to number 0 to 9 on the keyboard) (values are therefore 10 to 19).
Other events check if the variables' value correspond to the note then a sound is played...

The problem is, it seems that the engine doesn't allow two or more keys to be pressed at the same time, even if paired with different variables.
Therefore, I cannot play two notes on the piano at the same time. I can only play notes in quick succession at best, which screws up the whole system because I want to allow players to play any song like they could do it on a real piano.

When two or more keys are pressed, only the one with the higher value is considered. For instance, if I try to play Do and Mi at the same time I press keys 1 and 3 on the keyboard, but only the "Mi" sound plays.
I want both "Do" and "Mi" to play at the same time.

Does anyone know if pressing two or more keys at the same time on rm2k3 is possible? If so, how?

Thanks.