I'm having a really hard time with: "Power cable reduced my soundstage"...

If you hear no difference with a more expensive cord then that’s fine. I personally tested an AQ Hurricaine on my Niagara 7000 and was stunned by the upgrade in sound. Can I explain how it works, no. Do I believe it works, yes, for sure.

If you don’t hear power cords it’s OK. A lot of people don’t. It’s a signal to noise thing as well as attention to detail thing.

Very few lobsters get out of the lobster pot. - Old audiophile axiom

May be boring but no one has answered the McIntosh amp cord question....

Many of us are aware of Ohm’s law and rectification followed by supply caps. As an arrogant engineer, I flatly believed that power cables wouldn’t make a difference since they supply power through a rectifier which generates DC on the filter caps.
Then one day I actually tried cables and conditioners, from Synergistic and later Audience, on my class-A monoblocks. I was amazed at the dramatic differences in that application and began to wonder how it could be possible.
I think the problem lies in our simplification of the system model. In engineering, we tend to simplify our models to a point needed to predict the basic function needed. In the case of power supplies, what’s needed is AC in and basic DC out. Exhaustive analysis of low levels of noise are often not addressed beyond basic consideration. The wire isn’t ideal, the power source isn’t ideal, the filter caps aren’t ideal. The process of rectification, generates a series of high-current spikes which are made up of a large number of harmonics, in turn generating voltage disturbances which can leak through the very non-ideal filter caps, and perhaps reflect back and forth between the source and load impedance of the system.