When I receive massage, it all depends on what the actual music is of course, but I love music with vocals in another language. I don't care what language as long as it is tasteful and flows nice for massage. To me it is beautiful to hear language without knowing the meaning of the words...I get to focus on the 'music' of vocals as an instrument. I think that is absolutely delightful and would LOVE to receive a massage with some of my foreign language music. For music with vocals in my own language, it would probably be a smaller window of music that would be acceptable to listen to for massage. I've got a Billy Holiday cd I'd love to have a massage to sometime. Her singing makes my whole being very mellow and happy.
I think that the mind can focus on whatever the mind wants to focus on whether that be the music or the feel of the sheets or what needs to be done after the massage or absolutely anything else regardless of whether there are vocals or not.
Anything can hamper the process.