If such a simple concept as increasing mass would increased frequency then more designers would use it. I know they alter mass with speaker cables. Almost every manufacturer charges more for the better speaker cables which all seem to have heavier gauge wire. In my own personal conversations with cable manufacturers they say purity of material spacing from one another as well as shielding, construction insulation etc are the critical component to obtaining optimum sound. I doubt they would all miss added mass and not focus on that if it was relevant.
I am in no way saying Schroeder did not obtain positive results. It seems he and others have experimented with a topology and antidotal evidence is showing some benefits in their systems. I am just wondering what the real reason for the results is. Can Improvement of the signal resulting in higher frequencies being reproduce by the amp be done in a more efficient and or cost-effective manner. Doubling up interconnect which are already expensive is pretty cost prohibitive. Especially when you need to do it between a phono, a DAC, a CD a tape machine excetera. That's a whole lot of cable and additional Hydra head behind your gear.