I have FINALLY implemented these fkin sounds. Even if the way i did doesn't really satisfy myself... Next time, i will try to add a timer to avoid too much sounds being triggered in a short period, and also try to move the system somewhere else in the code.. As for when an update of this system will come, i don't have any idea... I will surely continue to clean the code before diving into something else of this kind..
Ps: only goku has pain sounds for now, don't mind about vegeta in the video.
Added a condition to the system that checks if the character is dead. This way, pain sounds won't be triggered in death state (logic!).
Fixed online issues with pm->ps->lockedPlayer. Working great now. Thanks to warmelon who helped me with the tests!