The design will be more easy if we use build in li-ion battery like C421. the power is boost from +/ 3.7V.
In E12, the power supply does not need any boost and without any convert. in SR71X, the power is supply by 2 9V battery, that is one important reason that
they have very high sound quality.
so E12 will have great power, just say, do you think it will drive HD650 well?