Get the M20s. With the music that he listens too and the size of the room your friend will not miss that much the additional low end that the CDM9 NTs will bring over the M20s and the later should have far better mid highs. I haven't heard the M20s but they are often compared (and many people say they are better) than the B&W N805s which I own. The N805s have far better mid highs, imaging, detail than anything on the CDM series.
But you'll need stands for the M20s, btw, so count that too.
But you'll need stands for the M20s, btw, so count that too.