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

As the title says, I am looking for an exceptional preamp (obviously tubed) with warmth and liquidity, some of that golden glow, in the midrange and highs. I do not want slowness, or lack of detail, however. My budget is up to $6,000.00, for a used model. 

Based on my research, many of those that might make the list are very rare to find, and other recommendations would be greatly appreciated.