Power Cords


I currently have Wireworld Silver Electra power cords with upgraded Platinum plugs. I had two 1M Wireworld Platinum power cords, but rearranged my system and required longer cords. Yesterday I borrowed two Shunyata Sigma NR power cords. On the first note my wife softly said, "that sounds better". She said it was clearer. I listened for a couple hours, changing the power cords a couple of times. In my system and to my ears this is my conclusion:
The Sigma's are cleaner, definitely has more bass, a dead silent and completely black background. The Wireworld cords are more detailed, with a wider soundstage and better spacing/separation of instruments. All things considered I'll keep my Wireworld, but I'm curious to listen to other power cords.
After inserting the Sigma's I just don't understand how anyone that listened to different power cords could conclude that they can't hear a difference. There is a difference, but like any other component the individual has to decide if the change is worth it. $6K for two power cords is relatively expensive. Expensive, but oddly maybe a good value? In my system there was a definite improvement with better bass impact and articulation. Would spending $6K or just changing amplifiers yield similar results? As with most components there are trade-offs...is there a power cord out there that has the benefits of the Sigma's and Wireworld Silver Electra's? If so, at what cost?  
ricred1
Blindjim,
Thanks so much very taking the time to provide such a detailed to response. My plans are to get a home audition of Audioquest, Audience, and the Shunyata Alpha NR.
Although only for one day, inserting the Shunyata Sigma NR erased any doubt on the impact of changing power cords. The improvement in bass articulation was outstanding. Inserting the Sigma's gave me a better understanding of what is meant by a totally black background. All that being said, in my brief audition the Sigma's are on the dark side of neutral. Its not about what's better, but what power cord I prefer in the context of my system, within my budget. I will keep the list price at $3K and below.
Thanks to everyone for having a constructive conversation!!!
You need to be sure that the powercables you get are burned in. It doesn't make sense at all to listen to brand new cables.

The Hurrican were good even brand new. But when they were burned in they were playing at a much higher level.

You need to focus on the individual focus of instruments and voices. There are many American brands in powercables who have no F. idea hoiw smaal and direct voices and instruments are.

That is a main reason why we want to give demos at shows with real music and instruments to make people aware of how small and direct they are in real.

The AMT tweeter of the Pl-500 is abel to create a stunning level in diversity in height of voices and instruments. But most audio products and even cables are not precise enough to create this.
The older AQ powercables doesn't make sense to test at all. They are all inferior compared to the new ones. If you have an option try Purist Audio as well. 

In the past I did many tests with many different powercables. Often the Purist powercables were the best by far.
bo1972,
I honestly appreciate your input, NOW A BIG BUT. As much as I love my Monitor Audio PL-500's, there are speakers that I prefer over them. They are more expensive than the PL-500's, but my point is I don't want to get into this what you recommend is the "best" and everything else is crap. I know you don't want to hear this, but everyone hears differently and we can't isolate components, we are hearing them in the context of a system. Based on my brief listening of the Sigma's, if it had the same effect on another system and that system required more bass articulation and they valued a dark background, I submit the Sigma would be great. I will audition the Audioquest power cords and post my thoughts. 
I should add, after my audition I'm no longer considering replacing all of my cords. I'm convinced the right cord on my DAC and amplifier or power conditioner will provide the change I'm seeking.