Sam2, I don’t think YD 2:56 says that. What you probably thought he meant was the implication that it’s only b’veis hamishtaos, but if you look carefully, I think you’ll agree that he is referring to singing, not instruments.
In 137 he clearly assers instruments during Sefirah even when one is alone. He seems to hold that even the R”ma assers instruments to be played in public, so the additional chumra of sefira is for private listening.
In OC 3:87, he calls following the S.A. “raui l’hachmir” but “ein limchos b’yad hameikilim” to follow R”ma.