As Mijostyn knows, I too use Sound Lab speakers, the 845PXs. The "backplate", in Sound Lab parlance, is where the bass and treble audio step up transformers and the passive crossover network that divides the frequencies that drive them, are housed. In my speakers, the components of the backplate are highly modified to save amplifier power and to provide for a high input impedance favorable to my Atma-sphere amplifiers. Funnily enough, the Atma-sphere amplifiers in this system are driven by Raul’s 3160 Phonolinepreamp, most of the time, also by my Atma-sphere MP1, and sometimes by my BMC MCCI ULN SE. (The aforementioned Steelhead drives a Beveridge 2SW-based system in my basement.)
By the way, I think Mike Lavigne owns the CS Port phono.