Many good responses above.
Anytime an electrical signal passes through an electrical component or circuit or device, it will affect the music. Be it distortion adding, soundstage, etc.
The discussion regarding the amp (Audio Research REF 6) paired with the Bryston is a great example.
Each device has a manufacturer's recommendation regarding input impendence, output impedance, sensitivity, etc.
If you try to match a pre-amp to a particular amp without paying attention to the manufacturer's technical recommendations, you are asking for trouble.
this is like trying to pair a particular amp to a particular speaker without paying attention to the specifications and requirements.
The REF 6 is one of the best pre-amps made. I bet it doesn't match well technically to the Bryston amp and the specs probably indicate a mismatch.
Assuming that amps are amps, or pre-amps are pre-amps is the problem.
Of course different amp will affect soundstage. They have totally different circuitry. Not an apples to apples comparison.
And by-the-way, don't fall for the old solid state vs tube argument. There are some outstanding solid state amps out there that are just excellent. Just as there are some outstanding tube amps out there.
I have heard some crappy tube amps and some crappy solid state amps also. Totally depends on the design, construction, circuitry, power supply, etc. each is different.
It's funny. I'm a member of a Mopar car club. You know, Chrysler, Dodge, Plymouth. I restore classic cars and currently have a restored 1970 in-violet, 340 four speed pistol grip Plymouth Barracuda ("Cuda"). Anyway, People in my group always hype Mopar and with good reason and talk down about other cars. I will step up and say loudly, you mean to tell me that if someone gave you the keys to a 1963 Split window corvette you wouldn't take it in a heartbeat? They all laughed and said absolutely they would.
Tube or solid state. What ever suits your needs and likes.
enjoy