About synergy?

Synergy is sexual attraction between strangers; oh, wait, that's chemistry! ;)

Frankly, I'm not terribly impressed by the definition of synergy as a fortuitous assemblage of gear. My definition of synergy is more stringent, that being components which have been voiced together. This demands there be a design/electronic basis for the superior performance of the components.

I write about this in some my reviews such as that of the Coda CS Amplifier (at Dagogo.com).

There seems in the OP to be the suggestion that cables are a solution versus system matching of components. That would be erroneous; one must pay attention to cables as well as component matching. Cables will either be a boon to the system - call them corrective devices if you wish - or deleterious to it, so choose wisely. :)

As and avid audiophile for the past 35+ years and a current audio reviewer for the Stereo Times my feeling is that I can almost always get a better result by mixing and matching components for the best synergistic blend. Believe me I've played with loads of all kinds of gear over the decades and this has always been the case.

For example, when I used the VTL TL-2.5 preamp with the VTL ST-85 amplifier I found two amps that I liked better with the 2.5. And when I cable a system I've never used all the same cables (maybe brand, but definitely mixed the models for optimal results).

Although there have been times when I've used the same company's amp and preamp, or DAC and integrated amp with very satisfying results.

That said, I don't think I've ever stayed with a system where all the components (including the speakers) were from the same manufacturer. YMMV.

Yeah, I am the one who thinks that cartridge should be matched to speakers in addition to tonearm and phono stage. But it is a different kind of match, perhaps even more complex and subjective. And it doesn't mean necessarily that basic sound signature of the cartridge and of the speakers should be very similar. Depends very much on preference and music taste.
I generally agree that the best synergy can be achieved by mixing different brands though I try to stay with the same cable brand with the exception of power cords.

I have to say that to me synergy may be rather hard to quantify. For example, I have a Deja Vu Audio amp that I love. A while back I managed to pick up a used Deja Vu audio preamp at a great price and when I added it to my system the sound improved. But was it greater synergy? Or just a better preamp? Or perhaps a bit of both? So my advice is to experiment, and when you arrive at a sound you really like stay there. I have for about five years now and I find I am as happy as ever with my sound, especially after a recent retubing and cap upgrade, and I have I'm sure saved much money and stress getting off the upgrade train. Of course that train was much fun for many years, so ymmv. Good luck and happy listening though!

I'm really starting to hate that term, "synergy" as applied to audio. Misused subjectively. Prefer compatible and/or complimentary.