As you say it well , upgrading must not be motivated by only frustration..
We must learn the basic in electrical, mechanical and acoustical embeddings..
i learned it the hard way too...
Now i am completely happy with my 600 bucks system...
Upgrade is not an urge at all ... It is not even necessary because i felt no problems or limitations with my actual system...
But it is precisely because as you did yourself, i learned the basic , and now i am ready for the ultimate last and definitive upgrade at the lowest possible cost...Even if i dont need it, i know it will be a real upgrade..
This is the good news...
The bad news is my upgrades will cost me 15,000 bucks at least, it is much more than my basic actual system so satisfying it is... ... But instead of being in the minimal acoustical satisfaction threshold , i could be on the best ratio sound quality /price in the world ...( my headphone is really a top headphone )
--- To upgrade my low cost satisfying dac ( dac technology is now mature business low cost dac could be very good ) i will go with the complete new revolution in virtual acoustic room system for speakers and headphone by Dr. Choueri... I will buy his dac implementing his BACCH filters... Here there is no comparison with any other dac because the Choueri dac is a virtual room system patented by Choueri and not a standard dac with NO DEGRADATION OF TIMBRE ... ( i trust acousticians 😊)
--- for amplification i will go Atmasphere D amplification because i trust his craftmanship or To Benring tube ZOTL... I dont know which one for now.. But for sure they will beat my old astoundingly good Sansui alpha...I cannot imagine that Atmasphere and Berning will created inferior design... i am in faith here reading about them... i dream as i said because i dont need upgrading, but being an audiophile is a bit neurotic and dreaming about the best in the world... You know that i think..
--- And nevermind any other headphone i will keep the AKG K340 because i cannot fault it now and i dont know at all how to upgrade it with improvement on all acoustic factors at play and not only on one ? Because of his unique technology in headphone history his soundfield is unique... it is a creatuion by an acoustician physicist founder of AKG... Then i will keep it... I had no idea how to beat it anyway...
Thanks for the interesting thread...