I am currently in the process of doing this wiring and in fact just today installed the 20 amp breaker in the panel and pulled and tacked the 8-gauge from the box up through the attic and to the wall where it will come down to the entertainment center.
I still need to come down through the wall and will probably just cut and remove the old 15 amp wire and use that as the wire pull through the wall.
All plugs are 20-amp hospital grade (with the green dot) and will accept the 8-gauge wire.
We have solar panels and an inverter. I’ve heard that these can add noise on the line. I put a ferrite bead over the wire right where it comes out of the panel. May not help anything..., but couldn’t hoit.