Well, you don't mention the exact location of your panel.
Yes, you can install any number of outlets next to your panel.
Be certain that they are all connected to the same phase.
Since they are for your audio equipment "ONLY", I would consider them to be dedicated use outlets.
Meaning that they are not considered convenience outlets.
Convenience outlets, depending were they are located, may have to be ground fault or arc fault protected.
The extension cords are a gray area, an item that's probably going to be left to interpretation, but I would say that you are connecting cord connected equipment with a cord that provides a means of disconnect at the equipment.
I would use high quality #10 AWG extension cords.
Then there's always Wiremold surface raceway.
When in doubt contact your local authority having jurisdiction. NEC or no NEC, they will have final say.
Without actually seeing the situation, I may have said too much or not enough.
Yes, you can install any number of outlets next to your panel.
Be certain that they are all connected to the same phase.
Since they are for your audio equipment "ONLY", I would consider them to be dedicated use outlets.
Meaning that they are not considered convenience outlets.
Convenience outlets, depending were they are located, may have to be ground fault or arc fault protected.
The extension cords are a gray area, an item that's probably going to be left to interpretation, but I would say that you are connecting cord connected equipment with a cord that provides a means of disconnect at the equipment.
I would use high quality #10 AWG extension cords.
Then there's always Wiremold surface raceway.
When in doubt contact your local authority having jurisdiction. NEC or no NEC, they will have final say.
Without actually seeing the situation, I may have said too much or not enough.