Belin- You think every halacha that has no straight out source in the rishonin is a Chumra? What happened, you think the 16 achronim invented this by themselves? No. pshat is like Reb sam2 said. There was a gezeira from yemos harishonim not to get married. The shayala was can you make a seudas eirusin. Zugt the Magen avraham, YEs you can make a seudas Eirusin. But be careful to be extra makpid on Rikudim but you want a kli shir, noooo no that is too much of a pirtza. So say all the achronim OK it is then a huge Kal Vchomer that stam Not ltzorech mitzvah Rikud or kli shir is assur gamur or as reb moshe says more assur than it is the rest of the year.
And who is this Mekeilim that we go after? I don’t think there is a source for the mekeilim. You found somebody meikil?
It is a kashya on them. To have a BERLIN style attitude I will say why can you detract things from a halacha without a source?
And if a tape is a kli shir? c’mon can’t figure that out? KLI SHIR- a thing that makes music. End of story