If I remember correctly from my talk with Steve, the new passives are dual-articulating and/or dual-tuned. I don't think it's as simple as changing the mass of the PR. Of course, I've been wrong before
Question for Steve/Ziggy: Have you guys tried tuning the left and right side of the speaker differently? ie, different length port on the left/right sides, and perhaps keeping the original PR on the left and putting the new one on the right? Sorta same idea as offsetting a driver in a baffle to average out peaks in the response? Or perhaps this is un-necessary and/or would just screw up the tuning and sound?
I was just thinking this might be a happy medium for any in the mentioned 10% that like better the un-modified/stock version of the HDT.