i think i have it. synergy in audio system is cooperation among the components of an audio system producing a sound, which you the listener likes.Point, game, match...to Mr.Tennis.
thus if you and i are listening to the same stereo system, we might disagree as to whether synergy exists.
However, synergy is in the ear of the beholder, and what one person thinks is synergistic may not appeal to another person hearing the same system.
And to his doubles partner, Tvad.