Hi Paul: one of the Decca's great strengths (and there are many) is bass power, which even its opponents concede. If you're not getting that now, then I hope anyway more mass will help. One thing for certain, the extra mass increases focus, SLAM/dynamics and clarity in the bass. In my system, with the slightly bass-light Klipsch Heresy's, I can't currently tell if it has increased reach. Try it, you might like it! One thing I didn't expect from a Decca being mounted on a Giant Direct Coupled Idler, is that now it sounds very much like a Grado (except with extra speed): rich and resonant and smoooottthh and organic. Never heard a Decca sound like THIS before! Very easy to live with. On belt-drives it comes across as more speed and detail-oriented, and in your face. Idlers suit it!
Yep Peter, they are horn-loaded as Rjdcan says, except the woofer: maybe this is the heresy! Apparently, PWK named the Cornwalls for the fact they were to be placed in the corn-er, against the wall :-).