Will an after market PC improve the sound of CDP??

Yeah, that Diamondback will never help the amp, it's also a budget cable in the Shunyata line.
For your CDP, the Pangea line is so inexpensive and so much better than stock it's worth trying.

http://www.audioadvisor.com/Pangea-Audio-AC-14SE-Signature-Power-Cable/productinfo/PGAC14SE/2094/#.Uzozsscngt4

There's also the AC-14XL for $150 with 30 day trial. Also try looking in the archives to see what others are using.
If your Rogue cable is anything like mine, it's piss poor with no bass extension. I'm also in the middle of a PC upgrade and have been doing shoot-outs with several cables.

Give a Triode Wire Lab cord a try. Pete offers a trial period for home audition.

I agree with both Lowrider57 and Foster_9, PC's differences can be very noticeable, but are also very system dependent. Aftermarket PC's can vary the sound quite a bit, just as much as interconnects, though I would not always call it an improvement. Different is not always better. You have to listen for yourself.

In my experience yes I have heard an improved sound from an aftermarket PC on a CDP in my system. When I heard this was with a MAC (My Audio Cables) HC Sound Pipe power cord installed on an Emotiva ERC-1 CDP. This was with budget gear so people's mileage may vary. When I moved the MAC HC Sound Pipe power cord to my 1st generation PS3 I believe I got an improved picture and SQ but at the time of that change I made wholesale changes power cord wise and power conditioning wise in my system. So yes I believe a PC can improve the sound of your CDP but again trial and error may be required with potentially more expensive power cords or with different wiring types.

Best of luck.

Sunnyjim,
The cost effective way I remain satisfied with is to use a Mapleshade Records Power Strip/Conditioner which improves the sound of the components whose individual PC's are plugged into the Power Strip/Conditioner (there is no power limiting so even an amp can go through this strip). There is much more chance to hear a gratifying and obvious improvement when each of the PC's is simultaneously upgraded by this cost-effective method.

Into the adjacent AC plug is inserted a Machina Dynamica RFI blocker called the Flying Saucer by the manufacturer. This tiny cost item should continue the upgrade even more.

This all yields a simultaneous improvement in each component's performance, with some of my components having hardwired PC's and some using individual removable PC's. You can still make an individual CDP PC purchase for further individual upgrading, but the starting baseline system performance already sounds better.

This addresses your wish to help your CDP sound better, as it simultaneously helps each part of the sound system chain from source to power amp stage.

There are also multiple ideas from various Audiogon sellers to allow better "reading" of the CD data independent of your choice of PC. As you know, my postings sing the praises most loudly of ideas from Machina Dynamica and Mapleshade Records.