Should I upgrade power cord for my preamp?

assuning that you have a quality built component .... In a word: Absolutely .....(emphasis added) Along with your source(s) if not already done.

Upgrading the PC to your preamp can make a huge improvement in performance. However, each aftermarket PC is different and it may take several attempts to achieve the timbre that pleases you.

I believe cables should be thought of as a component in the system. My advice is to try a couple from a company like Audio Advisor, who has a 30 day return policy.

It's important for you to use a cable that is rated for low-current components. IOW, you don't need to buy the same cable that your amp is using. IME the heavy gauge cables will have a negative effect on a preamp.

Yes. Lowrider has a great point about AA. You can't go wrong.

Get a STEALTH V12 upgrade asap.

Audio Advisor is a nice resource. I have bought from them indirectly via Amazon for same cost plus I get points on my Amazon credit card when I do it that way, which adds some value.

I love their catalog. Reminds me of the old Lafayette or Radio Shack catalogs except targeting good sounding audio, and no low level parts, like resistors and capacitors, though I think you will find a fuse or two maybe. :-)