well…..first what a wonderful position to be in..those are two awesome and fantastic preamps to choose from. I am certainly no stranger to either including your downstream components - i run the 7 mk2 and RV’s 7 high pass amplifiers. The pairing of M5 and Kento is super nice. I also have an ARC ref5se and Jim Whites ( of Aesthetix fame ) Signature DAC… so I get an appreciate tge Aesthetix sonics and construction. Up to me, i would go ARC but we are splitting micro hairs here for sure…
i just helped a friend w M5, Quattro and he chose the Aesthetix pre ( used and upgraded to signature but not eclipse )
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PM me if i can be of any insight or help
Jim