Have you configured your system as 2.1? Beyond that, what is the source content you are playing? If the source material is 5.1, LFE (the .1 channel) should go to the sub no matter how you configure the L/R speakers. If the source material is stereo, there's no LFE channel and you have to engage bass management so that the receiver will redirect low frequencies from the main channels to the sub. That's done by configuring the speakers as Small.