I have a fair bit of experience in wiring up the type of installation you're talking about, Here are some of my learnings from those experiences.
Some heavy duty cables used to run from fuse box to socket never sound right. They sound like they need to burn in but they never do.
Even the best cables will initially sound bad and will need time to burn in, so how do you know if your cable is 'hi-fi suitable' or not? You don't, at least not without ca. 100 hours burn-in, so you need to use 'audiophile approved' cable i.e cable that other audiophiles have reported as suitable for hi-fi use. This will almost certainly cost you more as a. its better cable and b. its usually obtained through specialist stores serving audiophiles so pricing is premium. Is it worth it? Depends how you feel about getting the whole job done, then waiting for it to sound better while all hope slowly dies after spending 200 hours listening and waiting for your system to begin sounding good. My advice; buy cable known to produce really good sonic results. You'll be happy you did long after you've forgotten what you paid.
Next sockets. At least in the context of my various systems, they always sounded better when they were fed from a single, suitably rated socket. This automatically implies the use of either a mains block, a hydra-like device or a dedicated mains conditioner. A poor quality mains block will completely destroy SQ, so again you need to go the 'audiophile approved' route. Typically such blocks offer much better contacts for improved plug grip and equal resistance between all earth points. The latter is critical as all you need is one component sitting on a high resistive earth to ruin your system's sound.
When all is done properly, what can you expect?
No more mains-borne switching transients. All aspects of the sound will improve, some of which are just 'more' like more bass, more treble extension and sparkle, wider deeper sound stage and some which actually fundamentally increase listener involvement, like more pace and rhythm, so higher boogie factor, less harshness and grunge and greater 'musicality' and clarity.
Proper mains supply is one of the most important upgrades you can do, but it must be done properly to realize all the sonic benefits.