In my experience, shielding tends to close in the sound (although some system really need it). If with this new cable (op) the soundstage is reduced it could be that some hum is coming through and screwing up the perception of "air" and "placement".
I'm having a really hard time with: "Power cable reduced my soundstage"...
My good friend that is in the business and very very knowledgeable calmed that a well made 10ga power cable reduced his soundstage... I'm not saying it will or won't but why would it? I would like to know the science behind this. I did research on here but not satisfied. I had a pair of Logans and they were wonderful and I used stock power cables and the stage was crazy... I have been making cables for years ( musician ) and know the value on quality... what is the magic?