But have you set up the amp to say the front speaker "are" Small, rather than Normal or Large? If you leave them on Large then stereo bass is not sent to the subwoofer no matter what setting you have for the filter. When you select stereo on your amp do you see 3 channels activated, or just the 2 main speakers? On my Yamaha amp the little GUI image shows what speakers will be used, not what the source is. So if I set Large for the Front, selecting Stereo just results in the 2 front speakers being shown. If I set them to Small, I get 2 front speakers, and the subwoofer shown.