Cap voltage

I took the lid off of my preamp today (Cary SLP 98) to poke around in advance of an impending cap upgrade. I was told by the tech that I can co to a smaller value on the output coupling cap ( might increase dynamics if feeding a high impedance load) but need to stay with 600v. ??? Why 600v when the pre only puts out about 2v. Don't smaller voltages sound better?