To some degree my passive sub has been a challenge, since purchasing it back in 1986. After reading about subwoofer performance enhancement strategies here, I resolved my big issue of getting the sub to deliver something not too small, not too big, but just right. Here's what I did: 1. for stereo music, any source, I am using my digital pre/pros DSP function to get sub output level and crossover relationship with mains to where it sounds right at the average volume level I listen to stereo music, 2. for multi-channel music, I am using the multi-channel source component's bass management feature for appropriate bass output to analog multi-channel preamplifier, and 3. for movies I am using my analog multi-channel preamp's channel level controls for bass management. With this configuration bass from stereo music, multi-channel music, and movies sounds so well integrated that I have not needed to make even the slightest adjustments; but, if bass level adjustment is needed, no matter the media, I can adjust by simply turning sub's power amp gain up or down. At any rate, what makes my multiple bass management configurations possible is my analog multi-channel preamp, which is set to bypass my digital control amp's output to speakers, and my OPPO's provision for bass management. Fun stuff.
