I think that Charles Hansen is a smart guy and a good designer. As such, he takes "real world" power conditions into consideration in his designs. I know this as he wrote a 5 part series of articles about RFI / EMI, AC noise, pole mounted transformer distortion, etc.. in Audio Xpress magazine. He's also contributed quite a few tidbits to that magazine, including a review of two different tuners in the latest issue.
As to the various power cords, i think that the Audience Power Chord works just as you say it does. I would say that its' greatest attribute is a very solid and well defined bottom end. I'm using them on my subwoofer amps for that very reason.
As to your preamp, try playing around with some high capacitance designs. These would be something along the lines of TG Audio, Kimber, etc... I'm sure that there are others out there, but those are what came to mind first. Sean
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