As of firmware 1.09 for the Plextor M6S, the Plexturbo (cache) software is now supported by this model... should be worth a try.
Until that version, it was not supported
Old system, Phenom II 965BE on M7A89GTDPRO/USB3 Win10 Current i7-3770 on ASUS P8H61-MX USB3 Rebuild i7-4790 on Z97-HD3 Various other old clunkers, 2x P4 also on W10