Dedicated 20a lines, 125 feet distance, which gauge wire to run?


Want to set up 4x dedicated 20-amp lines for my hifi system. The distance from the outlets to the breaker box is about 125 feet. What wires should I use? 10, 8, or 6 gauge? And should they be solid or stranded? If you could be as specific as possible that would be appreciated (brands, links, etc), as I am out of my depth here. The wire will need to run underground for a good portion, and then into craw space, if that makes any difference.
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Forgot to mention:

If you want to go down the rabbit hole that is researching 20 amp receptacles do a search on either Hubbell 5-20R or Bryant 5-20R.  There will be literally hundreds of options.  Check out commercial or industrial grade.  Or for the ultimate check out the hospital grade receptacles.

Secret  tip: many or most of the “audiophile” versions are just rebranded items from the regular electrical parts manufacturers with a commensurate price markup.
Use a subpanel absolutely. Use largest gauge wire to minimize wire resistance and voltage drop for the best results. +1 gs5556. Your weakest link will be the connectors, silver plated high grade outlets.
Awg 10 would be idea Copper, no aluminum wire 
awg8 even better but even high quality Gold copper outlets 
awg 10 is roughly near max .
Okay all, spoke with my electrician. We will be using #1 gauge from the main to a subpanel (I think 150amp subpanel?). And from the subpanel will be using 4x VH Audio 10-2 Cryogenically Treated Romex to outlets.

The electrician also brought up the idea installing a power conditioner at the subpanel. But I wasn’t sure how this would interact with my ability to use a high end power conditioner (e.g. niagara 7000) with my system. Any thoughts on this one? The electrician didn’t have a good answer for me on how an installed power conditioner may affect my system’s power conditioner.

As of right now, I told him to not install a dedicated power conditioner at the subpanel, but still have some time to think about it.

Thanks for everyone's input so far, very helpful!