The relevent section:
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Lefi Rav Moshe, Concerts should not be attended either. Also, Rav Moshe (here) is discussing live music, not taped. IIRC, there is an opinion that a tape/CD/MP3 has a din of a Klei Zemer, and should not be used even for vocal music.
P.S. The issur brought in Mishna Berura is specificly Rikud (dancing) and music that would lead to it (493:3), which seems to back the opinion of RSZA. (And yes, the Chofetz Chaim had “classical” concerts during his day as well)