Kenwood Excelon XR601-1 Reference Series Mono Subwoofer Amplifier Kenwood's Excelon Reference Series XR601-1 mono amplifier can power your subwoofer with up to 600 watts RMS. (That's a real world rating, not that inflated number you find printed on some amps.) An advanced circuit design and upgraded components virtually eliminate noise and maximize sound quality. Even better, the XR601-1 can fit into many different places in your car because of its incredibly low profile - it's less than 2" tall