OP, there are nine ways to Sunday to set a sub's volume. ryanosaur's advice is one way to do it. Another is simply to turn sub gain all the way down, play a test tone at the volume level you usually listen to music or movies and then slowly turn up the gain control on the sub until the tone seems to match front speakers in volume, or use a SPL app on your cell phone to appraise tone volume from sub is the same as mains. In this adjustment procedure start with receiver sub level set at factory default, or 0db. Thats' it. Now, note when you subsequently play music or movies at a very low volume or a very high volume you will need to increase or decrease sub volume to be pleased with the sub effect. That adjustment could be made via the sub's gain control; but, it is more convenient to adjust sub level from your receiver's remote if the sub is connected to receiver's sub preout. BTW, in my application, sub amplification is at 3/4 gain and Pre-Pro sub level is -2.0db generally listening to music at about 65db.