Or you could just use a Y connector cable. Install one set of ics to one set of preamp inputs and the other set of ics to another set of inputs. And if using a CDp for the source, and it has two sets of outputs better yet. For a truly blind test have someone else connect the ics to the inputs on the preamp so you, the listener, will not know which cables are connected which preamp inputs.
If the preamp is remote control, better yet for an A/B comparison.
If the preamp is remote control, better yet for an A/B comparison.