FWIW I had the 7BSST's in my system for a few years and recently heard the 28's and just thought they were more "balls to the walls" but very similar sonic signature. Now I have the Spectron monoblocks with Bybee and oil cap upgrades and would never even consider changing them for anything else (and I have had big tube monoblocks as well). Once you have the Spectrons, you only look to improve your system in other parts of the signal chain.
I did find however, that the Spectrons need a balanced power mains supply to be at their best and they will let you hear the difference between different power cords.
I did find however, that the Spectrons need a balanced power mains supply to be at their best and they will let you hear the difference between different power cords.