The single "subwoofer" cable will produce mono, even if you had two subs and you used a RCA splitter both subs would be receiving the same signal. To get stereo bass you would need two subs and use two speakon cables, one summed to receive the left channel signal and one summed to receive the right signal. You need to provide further information about your receiver, the line level output of your receiver is "meant" to connect to the low level input on A SUBWOOFER, remeber a rel is not like most subs. A REL provides this option for use with powered speakers, since you have an amp driving your speakers the hi-level/neutrik is desired and shoul be used. Don't use the low level and the neutrik together. Connect the SW output of your receiver with an RCA terminated cable to the .1/lfe input on the REL. You should be able to assign your receiver to output LFE through the SW Jack. If your reciever has a subwoofer crossover setting for the SW output make sure it's set as low as possible, I say this only if you are using the neutrik and .1/lfe togethr. That way you are utilizing the Rel crossover. Earlier you stated you main speakers go down to around 70hz, I see no reason you wouldn't want to use the speakon cable to suppliment them. And use the sw output of your receiver connected to the lfe on the rel for effects during movies. As far as a dedicated cable for the .1/lfe track, I would thinking investing in cable for that would not yeild better resulsts then the money spent to upgradIng to a better sub in rel line up i.e. a r305, r505 or a b- series.