Don Sachs customizes the Tubes4HiFi SP14 preamp.
The SP14 uses 6SN7 tubes. Cost depends on which options and tubes you chose; the base configuration starts at $1,699.
Upgrading the output caps to Duelund CAST PIO-Cu will set you back $375.
Upgrading one pair of the 6sn7 tubes to
Shuguang Black Treasure CV181z will cost $129.
Changing one set of RCA inputs to XLR is $275.
Worth adding to your list of possible candidates. The only problem is that since each one is custom built by Don, you can’t audition it before you buy (unless you know someone who owns one).
http://www.dsachsconsulting.com/custom%20line%20stage.htmlI own one and can attest that Don is a great guy and very easy to work with. He will work with you to ensure that the output impedance of the preamp matches the input impedance of your amp.
And yes, his preamp is an incredible performer!