it should be rca to 1/4" mono adapters...not stereo. This MAY be the problem. otherwise...how high is the subwoofer channel turned up on the receiver's calibration area. Simply turning up the subwoofer output on the receiver may do it. There should be one cable from the subwoofer output at the receiver to one side of the BFD. Also, what is the gain switch on the back of the BFD set to...+4 or -10? it should be set to -10.
If you haven't already read it, here is a great source of information on BFD setup:
http://www.snapbug.ws/bfd.htm
Sorry, just reread your post and saw you have it set to -10. Duh! I should have read a little closer before I replied!