I was wondering if i need to add a subwoofer to my existing speaker setup. I have Eltax liberty 7s as main fronts, and Eltax HT bipoles as rear, my centre is an Eltax LR. It's all quite bass-heavy, unlike say Mission speakers. When i bought the stuff the dealer hooked up a really small passive sub and the difference was negligable. But if i want to add a bigger sub, would it make a real difference? And if so, in what price range should i be looking?