The good thing about sound systems is that one can buy one thing at a time. There is probably nothing wrong with the Sony receiver. You need a subwoofer that has an amp built in, which happens to be most of them. The Parts Express subwoofers are the best value out there. If that does not appeal to you, get one from Best Buy. You can use the other speakers that you already have until you desire something better. Peace and goodwill.