... abit confused: how does a power cord affect the presentation of sound...

A lot of what is said is mostly true about not needing a 6k power cord with an exception of a couple of things. This is my take from competing in Car Audio Competition and from speaking to my best friend who works for Entergy as an engineer. The longer the cable run, the better the gauge needs to be. The only issue related to that is that our power lines every 50' or 100' utilize amplifiers to boost the power. This is why we have a major in-flux of power and AC noise. Hence why people utilize some type of power conditioners. Unfortunately when you use a longer standard cable with your amplifiers, you're asking the power supply in the amplifier to work harder and create more heat which is typically the enemy of sound quality. Shorter cable from the wall is better to reduce that. I'm my Roush Mustang, I use 2 gauge for my power cable to my fuse block  to 4 gauge to my amplifier and for the ground, I use two gauge but only a foot of cable for my McIntosh car audio sound system. In a perfect world a lot of what he said makes sense but unfortunately we don't live in a perfect world. I'd rather support the system in my home VS having to send them off to a repair shop due to power loss which hurts the power supply. You don’t have to spend a lot of money to get a good power cord to help protect your system. It all depends on the length you will need. In another words, how fare your amplifier is from the socket. Most standard power cords are 6 feet long.