@bache wrote: "I agree,, except one thing, like i say before, To get low bass like 30 -40 Hz using Omega Pro 15" woofer you need box very big 5-6 Cubic Feet . You can listen nice bass with smaller enclosure , but never get really low bass."
Very true!! High efficiency + deep bass = HUGE box!
In my opinion one possible solution is to design the system with subwoofers in mind from the outset. Only about one cubic foot would be needed for the Omega 15 (and a protective high-pass filter would be optional unless you want to go north of about 118 dB). You could then tailor your subwoofer purchase to your budget and room and SPL needs.
Duke