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.
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.