Oh my, this question is a delight to which to respond. I am a long time customer of Don Sachs who produces a 6SN7-based custom-made tube preamp in a beautiful wood cabinet. By far, it is the finest preamp I have had in my 45 years of having good to great gear. Don offers lots of options including a remote control, XLR connectors, caps upgrades from Mundorf Silver Oil, Jupiter Copper, to Dueland caps that increasingly enhance the performance of his preamp. The basic preamp runs around $1800 and betters the performance of preamps many times the cost of his preamp. Google "Don Sachs Consulting" for more information. This is my highest recommendation for a preamp.
Seeking Suggestions on Preamp Upgrade (CJ, Aesthetix, EAR)
I have about $5,000 budget to upgrade a preamp. I am using Luxman 550 integrated as a preamp currently, it sounds a bit too lean to me. Rest of the system are Pass XA30.5, Dynaudio Contour 3.4, Marantz reference SACD. I am thinking CJ CT5/ET5, CJ ACT2, Aesthetix Calypiso, EAR 868, or Zesto Leto. Thank you very much!