[JohnM]

Calibrate as usual once your filters are in place. Whether that should be 75dB or lower or higher is a topic that tends to attract lively discussion. A good way to set the sub level is to make a full range measurement through your AV processor with both the sub and a main speaker running, see how the sub level compares with the general level of the main speaker through the 500Hz to 1.5kHz range and tweak the sub level accordingly.