Best Tubed Preamp For A Warm, Rich Sound, Yet Still Detailed and Agile

second the recs for DeHavilland Ultraverve. Love mine. It's single ended only. 

Just curious, what caused you to leave the Model 6's behind, and what did you replace them with?

The never ending quest for audio nirvana.
I believe that I replaced the Model 6's with a BAT VK-75SE that I then had modified by Bob Backert of RHB Sound Dezign. The BAT is also long gone.
I tend to vacillate between tubes and SS amps. This time last year was a VAC tube amp. This year, so far, it's Pass Labs SS amps. Who knows what the future holds?

I've been married to the same woman for 33 years now.
However, when it comes to audio equipment, I'm not the "settling down" type.
I like to play the field. ;^)

Wall Audio Opus 88, I'm running it with a Pass Lab Volksamp 30 watts... I love the combo because they play off each other's strength nicely

Ck out the Cary Slp 05 with some vintage NOS tubes. Sylvania 6sn7 W circa early 1940s ot if you can find them, Tung Sol Black Plates. Very natural sound!  Quiet, quick, very musical.

You may look down your nose, but I got rid of an Ayon pre and kept an Audible Illusions Modulus 3a. It's very liquid, transparent, detailed etc. and you can get one for $2K or less. It's driving an MC275 VI (two mono), Maggie 1.7s and a Hsu uls15 mk II and I'm often startled by the presence, detail and timbre of jazz music, especially vocals.