[jdandy]

Ed.......There are two things to be gained with 10 gauge wire versus 12 gauge wire. The first is the rated amperage the wire can safely handle per the National Electrical Code requirements. 10 gauge wire can safely handle 30 amps. 12 gauge wire can safely handle 20 amps. Since you are using a 20 amp circuit breaker to feed the circuit, there is no additional current capability to be had moving to 10 gauge wire because the circuit breaker will trip at the 20 amp rating no matter the increase in wire size. Second, 10 gauge wire can be beneficial to offset a voltage drop that occurs on long circuit runs. A 50 foot circuit length of #12 copper with a 120 volt / 20 amp load calculates to a 3.4 volt drop. It is highly unlikely you will ever consume 20 amps on a circuit, particularly if you have two or more dedicated circuits to your sound system. A 15 amp load with the same wire size and distance calculates to a 2.5 volt drop. A 10 amp load with the same wire size and distance calculates to a 1.7 volt drop. 10 amp loads per circuit are far more typical of audio system loads than 15 or 20 amp loads. The point I am trying to make is you will not experience any recognizable performance gains by changing your 20 amp circuit to 10 gauge wire at the length you stated.

Ivan's post about the additional difficulty in terminating receptacles to 10 gauge wire is a valid point. Even if you are using the combination 15/20 amp outlets, the terminals are manufactured to accept the NEC rated wire size for the receptacle's current rating.

Hope you find this helpful.