I've found it helps to read to them passages from books about the conflict between thinking in words and visual pictures. Drawing on the Right Side of the Brain, etc. There are reasons instrumental works are more conducive to doing good work, "getting in the zone" as we call it, or "flow" as it is called in research. I have no luck allowing students to bring music without major conflicts, as the less mature of them don't understand why I would need to listen to it myself first, as they promise it doesn't have any bad words in it, which is not the only consideration. But once they have tried to work to music that is difficult to work to, they tend to appreciate the smooth, flowing instrumentals all the more.
But then, on Fridays, a little laid-back music from the 70's seems perfect, and my students like it too. Simon and Garfunkel is this year's crowd pleaser. Last year it was anything Celtic, which I can't even mention this year.