Unfortunately there is not a whole lot of grunge/metal recordings that will truly sound spectacular on a good loudspeaker - most were victims of the loudness wars in the past 20 years and will make linear loudspeakers sound bad . Pearl Jam albums like Yield are decent but not "reference quality". Albums from the band Porcupine Tree might appeal to his tastes and are well recorded which can be used as reference.
Its kind of tough to make recommendations without knowing all the different types of genres he likes.
