Benefits of brand synergy

I've had good experiences with matching the same brand amp/preamp. In one system I had with matching a McCormack TLC-1 Deluxe along with a McCormack DNA .5 Deluxe the music to me was heavenly. I also really enjoy the music with a Kavent S-33 preamp and P-3300 amp combo. To me I think the Kavent gear is supposed to work together hand in hand. I found the S-33 has a gain control. You can leave the gain as is or decrease it by 10db. From speaking to the dealers that sold Kavent they said the P-3300 has really high gain. I can't imagine the P-3300 without another preamp. I unfortunately didn't try it though. Sometimes it is the little things like that that make me think having the same preamp/amp combo is really supposed to be.

Totally agree that preamp/amp matching is the best approach. Have tried mixing sources with good results, but ended up matching the cdp as well, but only because it out performed my other.

I don't know about Naim, but usually good digital will work just fine with any brand decent electronics. As for preamp/amp, it is an interesting question which I believe cannot be answered in general terms, only on case by case basis. And also it might not be better or worse but just different. Within my price ranges I follow the path of integrated amps and don't bother about that.
Yeah, many mix brands to tailor the sound as precisely as they can to their taste. Given sufficient funds, time and patience, I would too.

There is benefit in synergy.

Buying all within a brand does not necessarily guarantee synergy, so careful there. Some gear in some brand lines together might provide it, some not.

Don't forget also that whatever gear you buy has to synergize with the room and your listening position as well. That is equally important, perhaps even more so. You might also have to buy trusted consulting services to get that part right if not comfortable doing it yourself.

(1). Using the same brand can offer freedom from technical incompatibility, take full advantage of "brand features", and possibly eliminate a better performing specific component(s), double up on brand coloration's, and possibly provide symmetry in shape, size and appearance which may or may not help with placement, is a safer route for novices and potentially compromising for experienced users.
(2).Using different brands can increase the chances of technical incompatibility, reduce the advantages of "brand features", maximize the possibility of using better performing specific component(s), counter brand coloration's, possible asymmetry in shape, size and apperance which may or may not make for more challenging placement, may be a riskier route for novices and possibly offer ultimate performance for experienced users.