Followup: I tried an informal experiment. My gear rack is on casters, so I repositioned it (from where it lives centered between the speakers) to a spot over to the side where the main AC cord could just reach both my normal outlet (now the Porter Port) and one on another wall that I don't normally use for the system. This other outlet is an old two-pronger like the one I replaced, and as with that one I used an adaptor to ground the connection. But this outlet is also on a different circuit than my usual outlet, so the comparison involves altering more variables than just the outlet quality and the use of the adaptor. (I moved one Quiet Line to whichever outlet I was plugging into, and doused the lights on that circuit.)
With the rack set up this way, I repeatedly auditioned one cut ("Dirty Old Town" from Rod Stewart's first album), played on CD instead of LP because my phonostage is battery-powered so I figured the digital front end could be more sensitive to powerline changes. Switchover between outlets was accomplished in under five minutes, allowing some time for the amps to re-warm. Upon first listening to both outlets, I was mildly surprised to think I did hear some slight differences, which I would describe as being between a more sharply defined, separated, brighter, and dynamic presentation with the Porter Port/normal AC line, and a more blended, spacious, mellow-balanced, and compressed presentation via the old outlet/alternate line.
At first I was almost thinking I might prefer some aspects of the sound using the alternate line (at least with that source material), but switching back and forth a few times made me much less confident that I was indentifying any real differences. I know this isn't an ideal way to test, but I quickly began losing interest as I became less convinced that there were any differences I could reliably track, or that really mattered. I could have been fatigued or bored, but by the last of about five rounds of auditions, I was ready to conclude that I couldn't tell the two outlets/lines apart by ear, or that if any differences did exist, they were too small and subjective for me to get worked up over.
So, I put the rack back to its usual position and powered-off for the night. Maybe I'll get curious enough some other time to try this again with more extended program material and listening sessions, maybe not...
