I have been using the abovementioned speakers since 2002 with no problem but recently the subwoofer is acting up. It "works" on and off, whether it is DVD or radio. I am using the Harman Kardon AVR2500 amp with the speakers. Is there something wrong with the LFE output with the amp or its the subwoofers that is acting up? Anyone with this problem too? Thanks for your advice.