I have a Shindo Auriges preamp with phono stage. It is the best preamp I have ever owned and I have owned a bunch
Shindo gear has cult like following, and is designed and best used in a system approach. Many users do however just use their preamps with other equipment. It has a very pure sound quality that is quite different from the majority of other gear, so is best auditioned before purchasing. They use minimalist circuit designs for the utmost in purity.
I have owned Shindo. It is very musical and beautiful gear.
However, I would caution that buying used you will get no support from dealers if needed. Some of the original tubes used are hoarded by Shindo and cannot be bought unless the gear was bought new from a dealer. Also, service, if needed is treated the same.
Having said that, the circuits are simple and workable by non-Shindo qualified techs. Tubes of the same likeness are available, just not the "Shindo" magic ones.
I run a full Shindo system, which is how it's been designed - pre - amp - cables etc... in a linked chain. Many feel (self included) that the Shindo's pre amps are the "heart" of the system. As you climb the line they just get better and better, where as the amps all have different personalities/flavors and should be auditioned based on your tastes and speakers etc... A Shindo Pre can be a game changer but you will never realize the full potential w/o a complete system and obviously you'll need high sensitivity speakers as well. To Muzikat's point about dealer servicing; I have heard that before but I bought all my Shindo gear second-hand and unknown to me a Shindo Montrachet amp I bought here via Audiogon was blown to bits by the previous owner. The importer Jonathan Halpern was so helpful and gracious in getting me back in action. Of course the amp had to go back to Japan and cost $2k in repairs but I have the piece on mind knowing that it was brought back to spec by the family that 1st made it. I fully agree with Bill_K, Shindo has a cult following. Like anything it's not for everyone but I've definitely drank the Kool-Aid.
While I own and highly recommend getting a Shindo preamp (Monbrisson) for the reasons mentioned above, I would be very cautious about Shindo amps with speakers of that sensitivity. I tried their 40 watt monoblocs with my 90 db speakers and figured they might work, as my 60 watt Jadis amps had been fine. Unfortunately, the Shindos just didn't work--dull, lifeless sound, very restricted frequency range. I had heard the same amps sound absolutely beautiful at the dealer's showroom, with more sensitive speakers, so I knew what they were capable of with the right speakers. If you want to buy Shindo amps, you really need to try the amps you're interested in with your speakers before you buy, as I did.
Also, Shindo preamps as a general rule don't really seem to work well driving long interconnects, so if you have anything longer than a few meters between the preamp and amp I would again suggest an audition before buying. I didn't get my Shindo preamp until I moved to a smaller room and had shortened the length of interconnects to the amp to 1-1/2 meters.
No one could argue with your sound advice, home auditioning if possible is always the ideal way to proceed, problem it's often easier said than done. I am somewhat surprised that their 40 W amplifier would struggle with a 90 db speaker, it raises the issue concerning power supply stiffness and output transformer quality (I would expect top quality from Shindo). I have used a 40 W push pull el34 amplifier with 91 db sensitive speakers(12 ohm) in the past with no problems, it was a very good match.
Shindos really (REALLY) like Living Voice Speakers (they are 94db). Thats a marriage made in sonic heaven. In Living Stereo (NYC) had a shindo preamp/amp and accuphase cd player going into a pair of living voice speakers (18 years ago) and its beeen the one of the best systems (still) I have ever heard.