My dad has just purchased a cheap Yamaha 5.1 speaker set from Richers to rig up to his old 'Dolby Pro-Logic' Kenwood amp (a bedroom set-up). The problem is that the amp has no 'subwoofer' output and the speakers really need the sub to provide the bass. Is there anyplace I can purchase a 'cross-over' which allows me to connect both front/left and front/right channels 'into' it, splits the lower frequencies to a 'subwoofer' output, and then has left and right outputs so the stereo signal can carry on to the front speakers? The sub has 'left (mono)' and 'right' phono sockets. Thanks on advance. Scott.