Hello everyone 
In relation with this topic, I figured out that my solution was not correct because the SoundEffectInstance seems to be played on another thread, and I compute the current sound time in each frame of the main thread, which can give me a wrong one.
The idea would be to retrieve the current time directly from the SoundEffectInstance, but there is no method for that in this class actually. But looking at the code on Github (here), it appears that there is a way to get the Sound instance used. And the Sound class has a getter for current time! (here)
This code is here since 7 years, but what I was looking for from the beginning was a fork of MonoGame, and the SoundEffectInstance doesn’t have a way to retrieve the Sound instance anymore (here).
Do you know why we can’t do this anymore? Is there a way to do what I want?
Thanks in advance