i should clarify, compound spring systems with TT, when they exhibit reinforcing fundamental resonance frequencies are bad in an obvious and often woofer puking way. i don’t think you are doing anything wrong Steve to wit your good sonic results.
i based my comments on real world experience w a 6 degree of freedom base miscalculated for TT mass on a minus K system, only a quick hand ( not mine ) on the volume saved the speakers....
Steve - what are you using for shelves ? i need to change mine at the condo