I've been thinking about what is meant by 'synergy' with regard to Hi-Fi.
Dictionary definitions of the word synergy say it is the interaction of 2 or more things giving a combined affect greater than the sum of their parts.
This definition makes sense. I am not an expert with electronic terms and definitions so some of what I understand will be wrong.
Just on amplifiers: 2 amps from different manufacturers may measure almost identically (flat frequency response) when presented with an 8 Ohm load so should perform the same.
What happens when they are asked to drive a pair of speakers though?
Speaker impedance ranges from far below to far above 8 Ohms.
One amp may cope well, the other may not.
There are multiple interactions – source to amp, amp to speakers, speakers in room, room layout.
Synergy is when you have all these components working well together to produce an accurate (as far as possible) rendition of what you are listening to, perhaps beyond what they should be capable of given their specifications & price level.