For loudspeaker cable comparisons you would need a microphone.* Don't touch that dial! (the volume control) and do your two tracks. We don't want to equalize the level because that might be part of the difference between the cables, and we want to know that information.
Other fun things to try: examine "Break-In" of components, cables, loudspeakers (your second track, obviously, would be recorded after x many hours of run-in).
Check how clean your power is; run the first track at high demand periods (usually supper time or shortly after) or when you suspect your neighbour has his X-10 devices operating, and the second at, say, 4 AM when there is little demand on the grid.
See if your system needs a "warm-up" time before it sounds best; first track upon startup, second track after 30 minutes (or some other value, if your ears suggest one) of playing music. That should be another test requiring the microphone.
Layout of signal cables vis a vis the AC line cable; try different lays and see if the hum / noise /RF goes up or down.
I'm sure someone can come up with more.
* Ideally, you would make all comparisons via microphone, so that your entire system is part of the equation, since that is how we listen to music. But it's possible to do so without a mic in some cases, and probably won't cost you any money to do some basic testing as you may have all the interconnections you need at hand.