Thanks @Anke @Patryk_F @TIMAI2 for your precious support; but in the end I simply thought of using Audacity to split the 7.66 Mb Mp3 file into two parts, the first of 3.64 Mb and the second of 3.93 Mb. Good evening
As I said several times, adding files larger than 5MB to assets is not a problem when doing it with 7-Zip or WinRAR.
So what's your problem?