If your cable is of sufficient size gauge and well put together your off and running. A percent figure based on the quality of your system (rule of thumb) is Total BS. Better components if you’ve cash to spare is the way to go. As said a million times build / set up your sound room as to compliment your system. Again having well made proper gauge cables should be the end game, that said PC’s will do Nothing to the tonality of your system !!
Cheers