Troubleshooting Wii U-Sing and We Sing

I have the same problem as everyone else - the microphones do not work in a duet!
Of course I had inquired in advance whether it is suitable for duets and I got the information, that for example "U-Sing" is not listed with, because it is still too new.
However, since it is currently almost impossible to get 2 microphones for Wii (WITHOUT U-Sing, etc., which I had already), I sent an email to the manufacturer. First, they advertise that the microphones are compatible with the Wii and on the other hand, we also have a PS2, so we could use the microphones for both devices - theoretically.
-> So how do you solve the problem with the Wii?
Now I got the response that is needed for this purpose a second adapter and they are willing to send me this when I tell them my address.
This I have done and am very curious to see if it works then.
However, as I go out of it, that I'm not the only one who has been annoyed and thus surely already several inquiries with the manufacturer have been received, I'm finally out of a happy ending.