Brand Synergy

The only brand synergy I know is that the face plates look the same. I never had a sonic improvement by matching a single manufacturers gear, quite the opposite in fact. 

@russ69 
+1 here.
and even more, some gear manufacturers comes out with a bold statements like for example “Great British Sound” in form of a sign on the face plates. Honestly, I don’t give a clue how they determinate this.

It can't hurt! Personally, I like to do it; I've got an MSB power amp, DAC/preamp, and Universal Disc Player, and Herron Audio phono stage and line stage preamps...

What is this synergy of which you speak?

For example the PS Audio BHK 250 power amp sounds good using a Direct Stream DAC. However it is significantly better with the BHK Signature Pre.
After that was discovered, further testing with three other DACs (one was the Denafrips Terminator DAC, the others not sold in USA) confirmed that the PS Audio BHK 250 was markedly better sounding to all of us at the meeting with the BHK Pre in the system.
Incidentally the Terminator was the best sounding, beating the Gieseler by a small margin and then by a larger margin the PS Audio DirectStream and another (I can’t recall the name) DAC was last.

The System was powered through a PS Audio PerfectWave PowerPlant 5.
The PowerPlant 5 was not removed from the system during testing.

We were confused, as the DACs used all have volume attenuaters built in, the idea of removing the pre amp made sense, in that by removing both an IC between components and simplifying the system it aught to remove noise.

We were not just a little surprised to discover the dependency of the BHK250 for superior sound reproduction, requiring the Signature Preamplifier. Simplification of a system, using highly resolving technologies, usually resulted in positive bump, and more often than not, more engaging sound qualities.

That Pre really made a significant difference, to the point that I wouldn’t invest in the BHK250 without it. I did purchase something else because I couldn’t afford both at the time of my amplifier upgrade.

@surfmuz - My CXUHD 4K Blu-ray player has a “Great British Sound” sticker that I didn't bother removing, however it generates a great picture :-)