Power cord that improve the soundstage the most?

Shunyata, Shunyata, Shunyata. The more you have in your system, the more the effect compounds. Not cheap by any stretch though.

Some of the cables are component specific; for example, diamondback and amps are a mismatch while the diamondback is great with digital. I would recommend a couple Taipan Helix cables to start with, well worth the investment imo.