I’ll echo the assortment or compilation theme.
I enjoy many genres. Consequently I should have a bit of each one that has distinct items I’m looking for a ??? to exhibit or demonstrate. Bottom end performance; midrange; top end finesse; sound staging; area of the sound stage; amongst these tracks I should get some pretty good idea of what to expect. I use Jazz, blues, R&B, folk, country, alternative rock, rock, acid jazz, choral, acoustic and metal. I have a couple tracks of Acapulco singers, male and female. Baritone Sax. Drums of course.
As said, I can’t see how someone could select ??? using but one sample of any music, unless that was the only music genre they listen to.
Put them onto disc and HDD, or bring along a couple LPs.