<font color='#000000'>Based on experience, an SPL (Sound PRessure Level()meter would help a lot. I am not aware of any fast rule on subwoofer volume position relative to the mains as these speaker and their amp charaterisitcs differ so widely. If your ears are accusotmed to hearing how the bass should sound relative to other instruments, then those ears are all you need to match them. Otherwise an SPL meter can be very helpful.</font>