“The chiluk is that singing w/o musical instruments is different than with musical instruments, it’s the same as singing shabbos zmiros”
So, again, R’ Moshe asks, who permitted music (as we know it – not acapella) the entire year. Perhaps we should be listening to acapella the entire year. To imply that the music we listen to all year is not problematic and the only thing under discussion is acapella during sefira and then imply R’ moshe agrees with this as well, doesnt seem correct from what I know of the teshuva. R’ Moshe still asks who permitted listening to music the entire year.
The Mishne Brura in sif kattan yud gimmel quoting the Bach is pretty clear about this too, unless you have a different understanding of this mishna berura/bach.