Power Cords

I second the previous comment about Signal Cable power cables. I've owned 4-5 of these, from top to bottom of the line--all sound great & are built like tanks.

Mine is a very good desktop system, not a full-blown audiophile system in living room, so maybe I'm missing something. But I've been more than satisfied w/everything I get from Signal Cable (that includes 1/2 a dozen interconnects, all excellent).

Hi ricred1. Have you unplugged all the other cords while you were testing Shunyata? The cords with different designs can interact sometimes as they introduce their own signatures (capacitance, inductance...)? Have you tried to listen to your system for at least 24 hours before switching to other tested cord? 
What I have realized while comparing an fantastic AQ NRG 1000 with Shunyata Zitron Alpha HC is that in every possible area Shunyata was better. Zitron technology simply made that jump over AQ.
I can not imagine what would Shunyata Sigma NR bring to my system, and I even do not want to think about it, as it is beyond my payment level in this moment, but if I had that money, I would rather think of investing into Shunyata Denali filter and used Shunyata Zitron Alpha HC. This would bring your system to a new level. 
Regarding here mentioned AQ new lines of cables... I do not believe it until I see it. I just believe my ears and testing of components in my system for a while. Maybe AQ really made something very good here, but let's first see it to believe it. 
When talking of Shunyata, yes, it can reveal a lot of low frequency information that you have never heard before, as it was masked, and yes, to some systems it will appear too much, as this systems that we audiophiles are assembling were carefully built to a level which covers for that part of frequencies which we are missing (which is now revealed by Shunyata)... so in the end you might think that you have too much bass. But in fact after Shunyata treatment, all of information (including bass) is revealed and clean and punctual, right as it is coming from from the wall or your power amp.
For example, I use all around Shunyata in my system, so in the end I do not need any subwoofer. I really do not miss this box which introduces new problems to my room.
I know that some power amps do not match some power cords (and signal and speaker cords). This is due to fact that some particular power amp and particular cable tend to maybe reveal more of one information and then the result is what? Probably emphasized one part of frequency.
It is down to Power Amp design and cords design... 
But to be sure if some power cord is good for your system, the tests have to be conducted well.
I must say that I've had non conventional approach in building my system. I first wanted to clean it out of AC and RFI/EMI noise. This was done by using Shunyata products all around (I have older line of Shunyata products), and then changed components as they started to reveal their true nature and signature. Some of components were kept, and some where changed. Now I am in phase where I am content with sound of my system, and really do not want to change anything.
Shunyata helped a lot in this quest. In reproducing realistic level of sound.
Well that is my opinion and experience so far.

Definately consider the Acoustic Zen line. I have used so many PC's over the years and finally settled on the Acoustic Zen Absolute cords. A bit pricey but well worth the $$$'s

I myself have found Audioquest power cords the best value for the money over the last few years.  Previously I had used Cardas and Shunyata power cords,  Eben today I find my 3 NRG10 power cords at $780 are far superir to any Shunyata power cord in the same price level.  I also have one 3 foot NTG1000 power cord which is far, far superior to the NRG10.  But I am also using 4 NRG100 power cords, which were superseeded by the NRG1000 about 2 years ago.  I was able to purchase 3 demo NTG100's for only $500.  The NRG100's are far superipr to the NRG10's, and are not far behind the NRG1000's.  Anyway soon, if I had the money I will be able to purchase demo Audoquest 1000's at a significant discount as a dealer in Ft.Collins who will be replacing his power cords with the latest models.  I am also using 2 Audioquest Niagara 1000's in my system, which make a significant improvement in audio quality.  I also find that a $400 JPS digital power cord works far better than any of my Audioquest power cords with either my Oppo 105 or 205.  And that is thru my Audioquest NRG1000 power cord and Niagara 1000 wired system.  Yes, a $400 JPS digital power cord just hooked up to either of my Oppo plaers is so much better than using an Audioquest power cord.  And again, that is thru an Audioquest wired system, thru an Audioquest power cord-Niagara 1000 aswell.  Just changing from an Audioquest power cord to my $400 JPS power ord in either of my Oppo players-the improvement in audio quality is immediatly apparent.  One would have to have severe hering loss to not be able to notice the improvement.

Power cords need to do two thing - supply enough current to th component and not pick up any noise/hash while doing that.

I've always thought that the component that shows the most effect from different power cords is the power amp, and that how much effect is shown seems to depend on the storage capacity of the amp. 

Those with modest power supply/reservoir capacitor capacity (talking about linear regulated power supplies here) are more affected by power cords than those with well regulated 'stiff' amps with plenty of supply capacitance. One of my class A amps seems to take no notice of what is supplying it - you can switch it off and it will play for about 10 seconds before there is any degradation of sound (and another 10 secs. until the sound ceases).

I used a tube power amp with more modest power supply to listen to power cords and found little correlation to price vs. sound quality.  My advice is to never buy power cords based on cost or reputation - audition them in your system to see if they make a bit of difference.

I have hard home made cords with welding cable sized conductors and hospital grade ends sound better than $1,000 'audiophile' cords.