Perhaps a different test could be tried using both mono amps and speakers thus:
Hook up one channel of the preamp to one splitter, then send both signals to mono amps and then to speakers. Put the speakers next to each other. Result is a duplication of one channel, but using different interconnects (or speaker cables if desired, but not both at same time). One speaker could be connected to each output (i.e. Output 1 Left channel, and Output 2 Left channel) of the amp. Simple switching between the outputs of the amp at a moderate listening level could yield quick comparison versus turning off the amp, swapping wires and establishing the signal again.
The differences in order to be efficacious must be immediate, easily heard. If not, then either the cables have very similar design, or one's ears do not perceive the differences. That's not a judgment, just a conclusion.
I find that some listeners have a difficult time with any delay in comparison, and they cannot retain very well what they heard. This setup would eliminate a long pause and make it easier to hear the result in an instant. I do not find that some systems are less sensitive to cable changes, but I do find that some are less resolving. The OP's rig is plenty good for this test.
With this setup the OP and friends might hear some differences, with various cables. If they still cannot hear the differences, then they should simply pursue economical cables and be happy. :)
Hook up one channel of the preamp to one splitter, then send both signals to mono amps and then to speakers. Put the speakers next to each other. Result is a duplication of one channel, but using different interconnects (or speaker cables if desired, but not both at same time). One speaker could be connected to each output (i.e. Output 1 Left channel, and Output 2 Left channel) of the amp. Simple switching between the outputs of the amp at a moderate listening level could yield quick comparison versus turning off the amp, swapping wires and establishing the signal again.
The differences in order to be efficacious must be immediate, easily heard. If not, then either the cables have very similar design, or one's ears do not perceive the differences. That's not a judgment, just a conclusion.
I find that some listeners have a difficult time with any delay in comparison, and they cannot retain very well what they heard. This setup would eliminate a long pause and make it easier to hear the result in an instant. I do not find that some systems are less sensitive to cable changes, but I do find that some are less resolving. The OP's rig is plenty good for this test.
With this setup the OP and friends might hear some differences, with various cables. If they still cannot hear the differences, then they should simply pursue economical cables and be happy. :)