20A is indeed what you want. How this "rectifies" with 15A components is simple. A is for amps, is for current. In the case of the dedicated line 20A is the maximum safe steady state current draw on that line. It does not mean forcing 20A into everything plugged in. It simply means that 20A is safely available.
Your components by the way are not 15A either. Not a one of them. Something like a CD player, phono stage or preamp draws only a very few amps. Power amps can draw more but even a very powerful amp comes nowhere near 15A current draw, except maybe for a brief moment when first turned on. One of the bigger power hogs in a room is a home theater projector, which if it has say a 500 watt bulb and runs at 120V then that's about 5A.
You want the 20A circuit because even though you don't need it in terms of steady state power draw you do want it because music is lots of very brief transient surges and the larger wire handles this better. Also the difference in cost is insignificant. Everything else, outlets, power cords, conditioner, is all the same 15 or 20.
Your components by the way are not 15A either. Not a one of them. Something like a CD player, phono stage or preamp draws only a very few amps. Power amps can draw more but even a very powerful amp comes nowhere near 15A current draw, except maybe for a brief moment when first turned on. One of the bigger power hogs in a room is a home theater projector, which if it has say a 500 watt bulb and runs at 120V then that's about 5A.
You want the 20A circuit because even though you don't need it in terms of steady state power draw you do want it because music is lots of very brief transient surges and the larger wire handles this better. Also the difference in cost is insignificant. Everything else, outlets, power cords, conditioner, is all the same 15 or 20.