I recently stumbled across the music of a gentleman named Ottmar Liebert, a guitarist. If you want to make the M60s sweat a bit, this might be your guy. Helps to define the "clear, transparent, forward" nature of the M60s. Knocks my socks off. I would stay away from his "Nuevo Flamenco" CD though - it can really pummel your brain cells. Do a search on Amazon, they let you try out a few tracks.