I have some regrets selling...

Anyone make an upgrade to their system, that truly did improve sonics, but (for whatever reason) you liked using the prior piece(s) better? (It could be looks, function, simplicity, etc.)
My uncle gave me his old Fisher 400 tube receiver (circa 1963) - real wood case, warm lovely sound, great tuner - in mid-1970's and I traded it in around 1980 for a really great (at the time) high end system.

10 years later I sought out a Fisher 400 and found one in good shape, had the "Fisher Doctor" renovate it. Very happy with my "retro" office system (Thiel 04a, AR ES-1)

Almost everything I've sold I miss.
Especially my old Dynaco ST-70 and my Pass Aleph-3
Miss my precision fidelity C7 preamp..cannot remember how I disposed of that; college days.
Ohm F speakers. I needed the money to go to Grad School and got what I paid for them and they were three years old at the time I sold them. They were a great speaker and I have wondered how they would sound with the front end and room I have today. Oh well!
In some ways, I regret dumping a mass market system I had many years ago. If I had it today, I could listen to it from time to time, to remind me that whatever problems my present system has, things could be far worse.
Threshold Stasis 7.0 Amp: A Power House from what I recall listening.
Yes, but learned from it as well. (Mac-ss amp, Supratek, Jas _both preamps.) Thought about selling my ML Aerius i but I can not get over the years of pleasure those stats gave me.
Besides......I still love the way they sound.