PX Series Power Amplifiers PX Series Power Amplifiers are dual-channel, Class D lightweight design with DSP onboard providing PEQ and crossover filters, delay and limiter functions controlled via LCD display. Presets are included for many Yamaha speaker models.are dual-channel, Class D lightweight design with DSP onboard providing PEQ and crossover filters, delay and limiter functions controlled via LCD display. Presets are included for many Yamaha speaker models.