What DAC upgrade made you say “DAMN, that sounds SO MUCH better than my last DAC”?

Had a Kora Hermes tubed dac since 2001. Still do. And love the sound it produces.
As a believer in power supply overkill and unique tubed analogue output stages in superior sound it hit the right ballance. It has two decent torroidal transformers one big one for the analogue stage and a smaller one for the digital stage also has a 2 volt and 5volt switch on back to help it fit in with a vast array of preamps.
I now have a Lampizator Lite 7 with pcm 356 and dsd 256.
I may upgrade it to big 7 mk2 status.
Imo these dacs leave behind everything in reference sound.
I could never buy a dac without tubes and certain aspects as many of these players, they are all cut from the same cloth imo.
When I got my Kora Hermes theyre were very few dacs available. 
A few names I remember were MSB, Meitner, Metronome, and to a lesser " also ran extent"
Theta, and possibly a few others.
But not like today where everyone has a flavor of the month!

PS Audio DirectStream DAC Sr. As others have said. I no longer yearn for Vinyl !

For me, I went from a Chord Hugo Mk 1, to a Chord Qutest. After 3-4 months I replaced the Qutest with a Denafrips Venus II with a Denafrips Gaia (D to D Converter) using I²S. My system is headphone only, my main amp is an upgraded Woo Audio WA5-LE Mk 1. At the time I purchased the  Denafrips (6 months ago), I replaced all cables that were not already Supra, with Supra Cables, mains cables terminated in Furutech AU connectors.
I have many, many tubes for the WA5-LE (at least 8 pairs each, of high quality, rectifiers, drivers and 300-B's).
Headphones are Sennheiser HD600, HD650, HD800S, Focal Elears, Audeze LCD-X's and Meze Empyreans.
The Qutest was very good, but the Denafrips made everything disappear, it just leaves the music!  My only regret is that maybe I should have gone for the Denafrips Terminator-Plus, but I'll never know since I can't audition it!

Audio Mirror Tubadour III SE I saw a very clear and substantial improvement, all other things in my system being equal.  Later I bought a PS Audio DirectStream Sr. DAC, it wasn’t as bright an improvement but it is clearly a better sounding DAC - in my system.

I heard the antiquated Philips TDA1540 chip with the Tube Output. It didn't rock my world when I heard it at my friends place. We did a head to head with my PS Audio DSSr. Tubadour III SE sounded thinner by comparison.

Tried a bunch of DAC's but my search for a DAC stopped after I put the Sonnet Morpheus in my system.