Manufacturers with great customer service

Sean Casey (Zu Audio) and Ralph Karsten (Atma-Sphere), both very helpful and informative (patient with my questions).

Zesto customer service is top notch.  

Mondial Designs (not only replaced a problem board on used unit, but tuned & cleaned everything)

Aerial Acoustics (talked to the owner himself for information)

Odyssey Audio (replaced faulty power LED nearly instantly)

Mapleshade (nice chat on jazz after responding to question)

T+A hands down, with IAG (Quad UK) a close second.

T+A is remarkably responsive and accommodating, willing to ship replacement parts directly to customers, along with (generally unnecessary) instructions for installing them.

I interacted with Quad numerous times in the 2000s, when I was involved with restoring a # of vintage Quad valve offerings -- tuners, preamps, amps, even ESLs -- to factory spec.  Very friendly, helpful people.

Wireworld Cables, Veritas cables, Oephi Speakers, Lyngdorf Electronics, Stack  Audio, Moonriver Audio. All the companies responded to my emails quickly and never appeared to be bothered with what I'm sure they thought were some stupid questions.