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

It’s no problem for me to use a junction box for say, 8awg, then switch to 10awg from there, as there is crawl space right underneath where the dedicated 20a outlets are going. I am going to use floor outlets. 

I have an electrician on site working on our house already. It is a new construction build, but maybe 90% complete.

So, a single 4-gauge from a 60-amp main to a subpanel. And from subpanel use 10 awg to outlets? Just to be clear, this method is preferred to using 4 separate cables (e.g. 8awg or 6awg) from main panel and using a junction box (instead of a subpanel) just before outlets?

Can you get specific on exactly what cables? Any specific brands and/or characteristics? i.e. Stranded vs solid core? Is there a solid core option for 4 gauge?

My electrician probably knows, but also I don’t want to assume anything, since this is hifi related and maybe he would choose something suboptimal.

Does more voltage drop also hurt sound quality? Or does it just affect how much total power my system can draw at a given time? 

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!

The power conditioner at the subpanel would work on all 4 lines, yes. I was planning to have the Niagara 7000 on it’s own dedicated line, with all electronics connected to it. And 2x MC901 monoblocks each on their own dedicated line. So, 3 of 4 dedicated lines allocated.

For the receptacles, I was planning on using 4x Furutech GTX-D NCF(R) AC Receptacles. Is there anything better?

I see, interesting. Do you have another receptacle brand you can recommend?