Thanks guys for the replies. I did not try what Blackmesa was suggesting coz' I know the sub is working,I ain't getting much of what I expected I guess, to imagine a 10 inch sub can do compared to the 6.5 of the Altec Lansing 621. I guess I'm expecting my room to rumble and thump in big bass sound that would come from the KSW10 sub. My room is small and not acoustically treated but I could hear good bass from the Altec 621 then. Anyway, will check again the connections and do your suggestions and see if there's any difference. By the way, do you think guys that the logitech Z-680 is better than the Klipsch Quintet w/KSW10 sub? just wondering.