Just wish to thank ROADRUNNER for your suggestions. I own the Onkyo TX-SR806 and have searched high and low for the answer re: playing music with a subwoofer. What worked for me was:

"..........If you are using only the left and right speakers in a stereo/sub 2.1 setup, some receivers will not output to the sub unless you have the settings correct. Be sure to set the speakers to "main/sub" or "main and sub" in the stereo multiplex section of the manual."

Thanks again.