Questyle cma400i balanced headphone amplifier and dac the questyle cma400i is a balanced headphone amplifier and dac a lovingly crafted and extensively tested product that exceeds all expectation design cma400i inheriting the state of the art technology of questyle golden reference system is visually impressive and mysterious for its black and sandblasted chassis and the amber light of led indicators cma400i can be placed straight with a specially designed stand which is not only space saving