The outcome of using the twinned interconnects, even when splitters or Y cables are used, supersedes the standard single interconnect. That has been demonstrated informally 8 or 9 times in my system, and with RCA, XLR, and once with an AES/EBU (XLR) digital connection from transport to DAC.
I am comparing some Y cables now, and upon recommendation from Taras at TEO have sourced some from Audio Sensibility. These are quite good and I aim to write up an article about the XLR and RCA Y cables from Audio Sensibility.
I strongly encourage anyone who wishes to try the Schroeder Method (Please do your due diligence regarding it being a do at your own risk method) to try at least a couple different sets of splitters or Y cables to find optimum performance. The time and relatively little money spent will be rewarded well.