Matching Gear matter to you?

As long as the piece of equipment being considered can handle (load, impedance matching, etc.) the other equipment, there shouldn't be an issue.

Then, it comes down to how it sounds in your system.  First, most companies don't make everything anyway.  Music servers, streamers, DACs, turntables, Speakers, cables, etc. so, there will be a slight mix anyway.

Also, just because a company makes say, amps, preamps and DACs, doesn't mean that they will be the best for the money you plan on spending.

so, it comes down to auditioning in your home and in your system.  If a dealer thinks you are a serious potential buyer (maybe spend quality time with dealers helps),  they will take your credit card information and loan you a piece (typically demonstration unit) for a few days.  

That has been my experience.  Also, there might not be many dealers in your area that have variety.  Sometimes they are stuck with only a few  manufacturers in house.  This limits your direct listening ability and comparison opportunities.

Sort of the Bose experience.  Bose makes it so you really can't compare directly their stuff with anyone else's in stores.

enjoy

Surely the important thing here is output and input impedances, and this is going to come into play most acutely between the preamp and amp.  Although a great many do, not *all* preamps and amps work well together, causing premature rolloff (p.r., an acoustic affliction) and other nasties.

then it comes down to what defines "better."  Synergies between products are very real.  Few other things to think of:

Does the off brand product have the right level of gain to match with your amp?  Preamps can have wildly different levels of gain and the appropriate amount is dictated by the amp.  Most companies preams will compliment the amps in the same line. 

What is the tube compliment?  Sometimes one product is better with stock tubes but when you roll in different tubes, another can excel.  In some cases, you have virtually no choice in what tubes you get. 

What sound profile are your trying to achieve?  There are a few companies that I can think of that produce tube preamps that sound solid state.  Does the off brand component serve as a substitute in terms of sound profile?  

One persons "better" is not another persons.  Are you sure that this other preamp is better?  Is there a technical reason why?  

Incidentally, doesn't matter if you answer these questions here.  Just want to provoke thinking to make sure that you are making the right choice.  Years ago, I bought a power amp not really knowing how finicky it was with preamp pairing.  I demo'd four preamps (amp in tow) to get one that sounded great.  Saved myself $1000 vs just going with the preamp from that brand and have no regrets about it.  

I like my (Silver) Schiit Freya preamp...I like it a lot...does Schiit make a single ended all tube hand wired point to point power amp? Since they don't, my little (black with gold front panel) tube amp will suffice, and it suffices the hell outta my music collection, as do the DAC with bespoke DC killing power supply (black), the phono pre (ditto power supply, black), the CD transport/player (black), and the headphone amp and Schiit Loki EQ, both silver and adorable...

I have had two occasions where the amp and preamp were from the same manufacturer and in each case they sounded better when i made a change .

First time i had a Mc Intosh C15 and 7100.  I took the C15 out and replaced it with a McCormack RLD 1     That combo was pretty good,  but I wanted to have a matched amp/pre so I bought a McCormack DNA 125 and it was even better.   As good as it was ,  I thought the preamp was the bottleneck, so I demo'd a Conrad Johnson Classic 2SE ....   the c-j / mccormack combo was really a great combo, in fact selling that DNA 125 was one of my big audio regrets.   

I still have the Classic and am driving some 40w Quicksilvers and I think Im at the point of diminishing returns .   That said if I were spending big $$$ to upgrade I would probably audition matched gear and would even consider a high end integrated, elimiinating preamp / amp matching altogether.