The primary purpose of a subpanel is to dedicate circuits to the audio equipment on a line that is as independent as possible from the main panel and other home circuits. The wire to this subpanel is just an extension of the wire to the main panel and the primary consideration is to minimize resistance, e.g., keep the guage at least one notch lower (larger wire size) that needed for the expected current. In my opinion there is no need at this point to worry about "audiophile grade". If this is done carefully, there will be no issues with ground loops or AC transcient feedback between componants, and the background noise level will be minimized.
The subpanel is where you want to start to implement your circuit distribution and power conditioning strategy. For example, putting each componant on a separate breaker with a separate ground, shielding wires, using hospital grade outlets, and considering an ISO transformer to reduce noise levels on the lines. All of these steps will increase the ability of the power supplies most efficiently produce clean and stable DC power to their componants. That is the goal.
The subpanel is where you want to start to implement your circuit distribution and power conditioning strategy. For example, putting each componant on a separate breaker with a separate ground, shielding wires, using hospital grade outlets, and considering an ISO transformer to reduce noise levels on the lines. All of these steps will increase the ability of the power supplies most efficiently produce clean and stable DC power to their componants. That is the goal.