Since you specified a used preamp around $750, I'm amazed that no one has listed the Adcom GFP-750. It's often sold used for $800-900, and is listed as a "Class A" recommended component by Stereophile. Even cheaper used is the Adcom GFP-565, which was a stunningly good preamp that now sells for $350-400. I owned the GFP-565 for a number of years, and it trounced a lot of preamps selling for up to $2K.
