Hi guys … just a small note for you … the Crown XLS amplifiers already include the low and high pass filters you need for subwoofer and surround setups. They can even be used for biamping speakers. It’s all in the setup menus.
Also, a sealed enclosure can theoretically go right down to 0 hz with the woofer cone just sitting there. The problem is that most people wouldn’t be able to hear much below about 30 or 40 hz, although we can detect a presence below that… the room will feel haunted.