hospital grade or commercial grade receptacles ?

Irvrobinson, you're a good sport (well, at least your wife's a good sport) to give it a try. FWIW, my personal experience has been that the most obvious changes are revealed when changing the source power cord. I have not noticed much difference when swapping cords on amps.

I second Tvad. Quality power cords on amps are low-priority in my experience--that is, if the amp already has something that's not the 18-gauge 3-dollar molded kind. Players, then preamps benefit most, and in that order.

If you have separates, the DAC would usually come before the transport in the lineup. However when I had my old Cambridge Discmagic / Isomagic pair, the transport's cord turned out to make more difference than the DAC's.

Irvrobinson...My dog says "woof, woof". Make what you want of this.

Hdm...I don't think that it is valid to compare a 115 vac wiring change with the Underwood mod to the Denon player. The mod involves replacement of a lot of active circuitry, and it is entirely to be expected (on a purely scientific basis) that the sound characteristics will change, for the better we hope.

When I tested the cryo'd outlet I put on my objective experimenter's hat. Believe me it would have been much more interesting if the test results had come out the other way. If anything, I was biased towards hearing an effect.

OK, the pre-amp and the CD player it is, rather than the amps.