One of the tools I use to evaluate equipment is a guitar or stringed instrument pluck. I don't actually have a guitar or stringed instrument to pluck, mind you, but I do have multiple pieces of music I use to listen to these plucks.
The plucked string is perhaps one of the toughest challenges for a piece of audio equipment to reproduce properly. Think about it. The initial attack of the pluck is a steep transient which tests the rise time of the electronics. The subsequent ringing of the string, followed by the decay of the string tests the harmonic integrity first, the low level detail retrieval second.
As you build your library of trusted musical examples from which to evaluate that new cable, DAC, amp or loudspeaker, make a point of gathering a few great string plucks for your arsenal.