All Digital LineupThe X-Power series uses much of the same digital technology as the PDX series, achieving high efficiency with excellent audio performance, including low distortion, high damping factor and high S/N ratio. Easily Upgrade Any SystemSpeaker Level Inputs let you connect these amps directly to factory-installed head units that do not have preamp outputs, so you can upgrade the original system with higher power and better speakers. Remote Sensing The remote sensing function turns the power on automatically when the amp detects an incoming audio signal. There is no more need for an extra remote lineSmaller FootprintPDX digital technology means high efficiency, so the X-Power amps are up to 29% more compact than previous models, making installation even more convenient. Effective Heat ProtectionIf interior heat reaches unacceptably high levels, a Thermal Protection circuit decreases power in two steps rather than interrupting the music. It also provides over-voltage and overcurrent protection. Remote Control Bass Knob (RUX-KNOB) Simply add the RUX-KNOB (sold separately) and get full control from the dash for instant bass adjustment. You also get the ability to control multiple amps from just one controller with simple telephone cord adapters