Preamp modifications - who would you use?

I am looking for a company or individual who performs equipment modifications to take a look at a preamp I own and recommend (and implement) parts improvements and or modifications to squeeze out the last bit of sonic performance. I would like to talk with someone who is well regarded not only for the quality of their work but also for their customer service, and who has enough experience and expertise to assess each piece on an individual basis, and not simply apply the same bag of tricks to everything they touch. Based on things I have read, folks that come to mind are Kyle Takenaga at RAM, Bill Thalman at Music Technology, and Chris Johnson at Partsconnexion. I would be interested in other recommendations. Thanks.