Well, i´m going to answer myself, maybe someone in the future will find this useful.
I have updated to the new 3.2 firmware (my pcb is 3.1), using the fw (for the 3.1 pcb) from this link:
The audio clipping in N64 unfortunately is NOT FIXED, at least in the 3.1 PCB.
It clips constantly with my N64. I have to plug the N64 audio directly to the TV or the receiver/soundbar to have decent audio.
Besides the new modes i didn´t see any other noticeable improvement. If someone is considering to buy the cable + pic programmer to fix audio issues, don´t even bother for the 3.1 PCB (at least in my opinion).