Mixed Brand Pre-Amp Power Amp Pairings that Work

I know that the performance of these two elements will be tightly coupled, so they need to match.

...

assume that they have optimally paired their own components to work well together

Utter bleedin’ nonsense 😲

Other than face plate esthetics, it 100% irrelevant. Assuming the gear was actually listened to and didn’t go directly from design to shipping, any impressions are only valid on the test system & program.

Change source / load / interconnects and room / program and any matching is toast.

And what anyone else has is 200% irrelevant for the same reasons. Best advice is to ignore every "I have..."

Many times better sound than two of the same brand.

I tried the same brand approach for elegance's sake and it wasn't that great.  

For me Cary Audio tube pre, Pass Labs Class A power. Amazingly good.

Backert Rhumba 1.3 preamp with Pass XA30.8 power amp.

Allnic L8000DHT with Pass XA60.8 on Mangepan 3.7i's.  Amazing but the input sensitivity of the Pass is 1.1V to full output.  I ordered a second set of low output DHT tubes but still can hardly get to 12 oclock on the attenuator.  Fortunately the Allnic has a constant impedance attenuator so it doesnt need to get wide open to sound its best.

I would have paid more attention to the pre-amp output and sensitivity of the amp if I had known to.  The Allnic is my forever pre-amp,  I am not looking to change the Pass amps at this time but if I do I will look for a higher input sensitivity like 2.6 volts.

Audio Research pre into Pass Labs X series works well