Connect an RCA cable from one of the RX-V667's subwoofer preouts to the LFE/line in input on the back of the sub. Turn the crossover knob on the sub to the highest level.
In the Yamaha options, set your speakers to small and subwoofer to yes if that option exists, as well as selecting the subwoofer for bass output if that options exists. Setting the crossover depends on the capabilities of your speakers. 80hz is probably a good starting point unless you have dinky satellite speakers in which case you might want to try 120hz.
