Brand Synergy

Good question.
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Brand synergy goes well beyond specifications. House sound is a very highly refined concept to all major audio component companies. They carefully craft their equipment to be complementary and achieve a bery specific sound.

I have been working on my system for over fifty years, high end audio was actually fairly new back then. It was just being organized as a thing and not a DIY hobby. In that time my system was largely a heterogeneous collection of gear. Part of that was technology... a budding company (designer) creates an inspired component for which they got great reviews. You bought that one. Then the designer would create additional products to flesh out the line. Like Pass amps (Threshold). Then created a preamp and phonostage. So, if you were to put together a really high end system you had to pick and choose different companies components. As these companies grew they were able to put more resources into development and as such develop a house sound... MacIntosh, Conrad Johnson, Audio Research, Mark Levinson, Pass... etc. Some companies have a lot of synergy... like Audio Research, MacIntosh. Over time, greater synergy was created as all of a company components came in line with the same level of performance.
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For most people speaker choice is a big deal. It can dictate amplification... that will lead to a different amplifier from the desired preamp. I originally chose a ribbon or electrostatic... and had to go with a powerful amp (I had no chance of affording an 250w ARC amp) but loved Audio Research preamps. So it pulled my brand choices apart.
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Finally income. I could not choose anything I wanted and compromises were necessary. But over time my income grew. So did my understanding of what I wanted out of audio and I was able to select what I wanted and with a little luck stumbled into the synergy that was possible... with all Audio Research gear. It is astonishing how significant it is. If I was starting out now... no question in my mind the easiest way to get to your ideal audio system is to listen to a bunch of house brands, choose the house you want to be in, buy entry level, and upgrade as your income increases. Note: speakers and electronics are likely to be different companies.

I recommend that. But the one really big problem is that your values change over time as you learn and experience reproduced music. So, maybe my story of convergence is the most likely outcome of the pursuit but not the usual path to get there.

A note on crafting sound for the consumers.
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One of the most interesting interview I read was with (I think it was this company) the lead designer from MBL... who explained that he can make a component sound like anything he wanted... you want warm and you use this brand of resistors, these capacitors, and this kind of winding... if you want detailed... you choose these. This company produces some of the best sounding stuff. So their top level equipment was designed for highly discerning consumers. But there was a limited number of them (with $30K+ per component), so he was designing components for a line that appealed to a different set of values (and smaller pocket book). So, crafting sound is way beyond specification... it is about crafting the character of the sound.
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I always suspected that true master craftsman knew their craft to this level. This interview confirmed it. One other thing... the choices in electrical components was minuscule fifty years ago compared to now. I was lucky enough to work in high tech electronics for the last forty years for companies that made components incorporated in high end audio gear... the difference is astonishingly large.

@surfmuzI “If Brand Synergy is being about to use one remote then just buy a universal remote?“

Good one!
Single brand is not a requirement but an advantage. I think it is now more relevant than ever before. Very definitely true for the larger high end audio companies like Audio Research, McIntosh, and Conrad Johnson. I’m sure others as well.