Can't connect more than 2 Joysticks

[vsilvalopes]

Hi !
I'm running sixad on a Ubuntu 16.04 machine, and it works flawlessly, when pairing controllers.

My only issue is when I try to pair more than 2 joysticks.
The third and the fourth one, simply won't connect.
The LED lights just blink, and the subsequent joysticks won't connect.
If I power off one joystick, the other pair successfully.

I'm using sixad based on the Retropie script.

Thanks in advance!