Main vs. sub panel for dedicated lines

One line. 10 or 8 gauge. 20amp breaker. 4 gang outlet. Distribution box.

Different philosophies regarding dedicated lines. Use one line if all your component’s amperage is less than the 20A breaker. The takeaway is no ground loop.
Use more than one line if separating digital and analogue, running high current monoblocks, or running subs. Lighting should be moved to other panel. Certain lights and dimmers will cause hum to audio system.

These circuits should be wired into the same leg (phase) in the service panel. In your current situation, dedicated lines should be run from the panel without the high-current devices. Although both panels will share hot, neutral and ground, the breakers are further away from the appliances that generate noise on the mains.

Two ground rods need to be drilled into mother earth according to your local code. The electrician will know this.

@noromance
8 gauge Romex will not fit 20A receptacle.

4 gang box is good idea if using one line.

@lowrider57 Yeah. I should have been more clear. That’s why I said 10 or 8. I run 8 gauge into a L6-20R which then feeds a 4 gang box.