The sonic differences that capacitors introduce into the signal paths are audible and measurable. Perhaps not to the extent that many "audiophiles" proclaim, but, as with ghosts, "I don't believe in them, but they exist."
I still own an old JBL LE14C cabinet; the original crossover capacitors were PIO 6 Mfd. Several years ago, I replaced them with Clarity Capacitors. Instead of 6.0 Mfd, CP manufactures 6.2 Mfd capacitors, so I installed those. After modifying only one of them, I placed the two cabinets in the center of my listening room, with the amplifier in mono, and after prolonged listening to various recordings—alternating between the left and right channels—I came to
my conclusion: more detailed midrange and treble, more controlled bass with CP. Better than with the PIO capacitors? That depends on each person's ear and taste. I didn't take any measurements, but I'm not one to doubt Clarity Cap's graphs. And when, after that experience, I built the Troels Gravesen DTQWTII, I chose the capacitor line that best fit my budget. Without hesitation.