The Monbrison's output impedance is 5k. I think you are mistaken about it being able to drive anything.
All of the Shindo preamps higher up than the Monbrison in the line-up do have low output imdedances that can essentially drive any amps because they have transformers that lower their impedance. The Aurieges, Aurieges-L and the Monbrison do not and, consequently, their output impedance is in the 5k range. You must be more careful matching amps with the Monbrison than a Massetto, Giscours etc.
All of the Shindo preamps higher up than the Monbrison in the line-up do have low output imdedances that can essentially drive any amps because they have transformers that lower their impedance. The Aurieges, Aurieges-L and the Monbrison do not and, consequently, their output impedance is in the 5k range. You must be more careful matching amps with the Monbrison than a Massetto, Giscours etc.