Overwhelmed and under experienced...

Seems like you've put some thought into your system, you should replace the cheap stock PC.
First, what is your budget? You've mentioned cables ranging from $300 to $625. When shopping for a cable, find dealers that offer a trial period and return policy.

A 10awg cable or heavier would be in order for your amp. If you like the sonic signature of the Shunyata then stay with the brand. Cullen Cables and Signal Cables offer well-built cables with return policies. VH Cables offers custom made Furutech and Acrolink cables at very good prices. They also offer their own cables with a return policy.

Look thru the archives using the key words "power cable" to see many more recommendations.

@erik_squires 
I do realize room acoustics play a much larger roll than most people realize, but this system is in our main living area and used daily. Thankfully there are a few helpful things going for it, large floor rug to help control first reflection, a few pieces of furniture, and curtains that are quite large for a roughly 7 ft. front window behind our seating area. 

@lowrider57 
Budget wise I would like to stay under $700 anyway. Not really sure where the point of diminishing returns would start to apply with my system.
The point of mentioning power cables from $300 to $600 was simply to mention I have come across some decent prices on good name brand manufacturer pieces (new and used) but also a couple unknowns that appear to be building quality pieces as well. Taking a chance on, and being happy with my Morrow Audio purchases keeps me open minded to the possibility that there are also the little guy/unknown companies that are out there doing quality work. 
I have been working with and purchasing from Jason at Thecableco.com. With one exception I have been happy with his suggestions so far. I have now also included an additional supplier as an option due to that incident. 
I have been through a few companies cables already. Replacing stock cables with Signalcable power cords is where it all started. Decent for the money, but couldn't get a good fit to component. Audience Forte F3 on the Marantz. Very nice sound but a bit too laid back. Almost as if the highs were s bit rolled off. Replacing the Audience with a Voodoo almost surprised me. Much better sound. More detailed with better separation of instruments. Issues with the Voodoo are that they are literally garden hose sized and only semi flexable. Low wife approval factor going on there. 
The one Shunyata I have used is the Venom HC. Definitely better than stock but can't really say it was super impressive on the amplifier. For the $175 sale price I paid away the time I feel it was easily worth it. It worked out fine though because it's now being used on the PS8. 

I don't know as if this reply will be much help but....
The Cable debate is huge and as I was interested in new power cables for I spent days reading many hours the opinions on this site and many others.  Of course, the recommendations varied almost as much as the answer to the best speaker.  
I have purchased power cables from Black Sand (very satisfied) and Morrow (used and with additional 40% off at the holidays a great deal).  Unfortunately, the improvement I hear may be due to confirmation bias???  I spent the money so God knows I want it to be for something.

Flip side is I asked the great N. Pass about power cables. 

" Large gauge oxygen free with clean connection surfaces are what I use, and I find it adequate. Keep in mind that I am evaluating amplifiers, not looking to explore the variations that specialty cables might introduce."

Food for thought

I compared the Shunyata Delta and Alpha NR cables recently. There was a huge change in the system by switching all of the power cables. Amps, Pre Amp and Line Conditioner and DAC. The system sounded different.

In doing an A/B/C shootout of Stock Delta and Alpha my GF and I decided there was huge improvement with the Delta and Alpha vs Stock. However we both decided that the Alpha was really dark sounding for us. Vocals seemed really far back. Almost all of our music is of the rock variety. We ended up selecting the Delta NR for everything except the DAC which we went with the EF because I could get the cable through the back of the audio cabinet. 

In talking with a friend that I made her on the 'Gon, his MIT brother suggested cables as the last thing to upgrade as each of them will color the system in a way that may or may not make you happy. 

I do realize room acoustics play a much larger roll than most people realize, but this system is in our main living area and used daily.

GIK Makes beautiful things.