Defunct brands-

I own a MFA Magus Pre amp. Though not in business anymore,

Scott Frankland still offers upgrades for it. 

He did some upgrades for me a few years back 

Yes, I have several pieces of B&K equipment, amplifiers and pre-amplifiers. I still love the sound. I used to own some Dahlquist DQ-20 speakers, they were ok. Sadly the company died with Jon Dahlquist. The main designer went on to found Nola Speakers as I recall. 

Cambridge Soundworks who actually had stores in malls to sell their equipment.  Bought equipment about 30 years ago.  I had a 5.2 system and a 7.2 system with a pair of 4 way towers with 300 watt amps in each to power the woofers.  After they went out of business one of the amps went and after several attempts at repairing it I sold the towers and center channel.  I still use 4 of the surrounds and I’ve replaced the 5.2 system with a Sonos system.  

Boston Acoustics speakers which were great in the late 80s and early 90's.  Dartzeel integrated.

Sonic Frontiers SFP-1 phono pre. I recently had Parts Connexion out of Canada refurbish and spruce it up. Replacing all of the caps with Mundorfs. The filtering caps were easily 5 times the size of the original caps. I replaced the tubes with Gold Lions. And now it is quiet as hell, sounds great, and will probably last another 30 years.