wire for dedicated 20 amp circuit

Maybe Romex is not permitted where you live, and that's why he came up with it. Ask.

Aluminum MC will better shield against power line noise from external magnetic/electric/radio fields. Probably the best off-the-shelf wiring you can buy for audio apps IMO. (Make sure all the conductors are sheathed, including the ground).

The only advantage Romex offers is ease of installation.

thank you very much for the info.

Uh, the LAST thing you want adjacent a dedicated line is a magnetic material, so at least use aluminum if it has to be metallic. RSVP for even better suggestions....