Finally, a thread I can contribute to ...
When I was auditioning equipment for my current system 25+ years ago, I compared Bryston and Levinson amps. I had a hard time hearing much difference between the Bryston 4B and whatever the corresponding Levinson was, especially enough of a difference to justify the huge cost difference. I also compared the Bryston 12B preamp against a Conrad Johnson preamp that was a little more money (sorry, don't remember that model, either). The CV was noisy to the point of interfering with my enjoyment of the music. The Bryston was noticeably absent from the sound, meaning it didn't add any coloration. These auditions were through Martin Logan Quest speakers. I purchased the 12B, 4B, and Quests.
Fast forward to a year ago. I finally acquired a pair of ML CLS IIz speakers. I hooked up my Bryston equipment and compared to the Quests, the CLS sounded edgy. I got listening fatigue fairly quickly. I put the 4B in my theater system with the Quests and got an ARC D240 amp. It is a much better match with the CLS as the sound is musical again. I love the CLS speakers; still some of the best speakers I've heard.
I just sent in my BP12 for an overhaul; second time in the 25+ years that I've owned it. I think it's a great preamp (others will no doubt point out preamps that they like better). It's got a nice phono stage for my moving coil cartridge (AT OC9) and I like having balanced outs for the amp. I find the music very engaging and lifelike in my rig.
When I called Bryston about the repair (wish I could remember who I spoke to), I asked whether I should consider upgrading given the age of the preamp. His response was "Absolutely not." When I pushed a little, he replied "Enclose a letter saying you'll sell it to the repair tech for $5 and I'll gladly take it off your hands." That made me laugh and reaffirmed my desire not to change a thing. No audiophilia nervosa here. :)