Excuse my ignorance, is DC on the mains such a big problem or something that depends where you live ? I mentioned it to my soldering sparky engineer mate and he says it is negligible here in the Canaries ( 4 decimal percentage) and that anyway if there is a transformer at the input it will effectively "block by ignoring" everything that is not AC. I have only 2 toroidals in my system but quite hefty ( Norton Air Power for my LP12 and the one in my Sugden A21Se) , the rest are R-cores or ad-hoc potted rectangulars for my phono stage. Worth a shot ?