Look at your system. If you have only two channel audio system , then one dedicated line for each amp and another dedicated line for the low level equipment (which should be all plugged into a conditioner/multiple power outlet device). So, for example for me, I have two amps each with their own dedicated line to the power panel, one additional line for my pre-amp, tuner, cd transport, music server, DAC (1), DAC (2)(don't ask), Turn table, phono stage, all plugged into a power conditioner/outlet device.
If you have a home theater system in the same room, then I would run an additional dedicated line solely for the home theater equipment.
20 amp lines with 10/2 type Romex is adequate, however, look at the manufacturer's recommendation for each amp's power requirements.
also, for electrical purposes, make sure the power lines are balanced on each side of the power panel. Example would be if you have two amps, then one amp on one side and the other amp on the other side to balance the house load. Any respectable electrician will ask for specific loads per power line to determine how to split the load at the power panel. Most homes in the US have 220-240 volt or so coming into the home and it is split on each side at 115-120 volts on each side. Then they split the house load on each side to balance the load.
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