About synergy?

I'm not clear on the question , but if the OP is asking if same brand same sonic signature is a way to obtain audio nirvana , the answer is likely no for most of us . If a preamp has a warm sonic signature than the last thing we need is a same brand power amp that is also on the warm side . Two warms don't make a right .
I have owned matching electronic's from Levinson , Audio Research and Ayre , all great stuff but all imparted there own house sound on the music . A variation with one major component can make it very difficult to hear that all to distinctive sonic signature . And it's never a crap shoot unless you purchase equipment without hearing it at length in your system .

Around these parts we use synergy to describe what you have, as all pieces in a system working together for a harmonious fit. Such as a speaker and amp working together (synergy) or that combo working well in a particular room ( synergy) or a cartridge working well with a particular phono stage... Etc...
Once you're aware of such systems, you'll know from then on if something is working synergistically or not. Well, some people seem to catch on!

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.