At the risk of sounding pedantic, a point of clarification needs to be made before anyone can really accurately respond to your question.
Consider: a true subwoofer (i.e., a speaker that handles the range below the woofer) is intended to handle the lowest octave -- from 20Hz up to 40 Hz -- and will usually overlap with the woofer into the second octave (40 Hz to 80 Hz). A speaker that is handling frequencies as high as 150 Hz is at the very limit of the upper bass range, maybe even going into the lower mid-range frequencies, and is thus not really a subwoofer, but rather a woofer.
Hence, you may need to re-think the woofer vs. subwoofer issue. If you really need to cross over at 150 Hz (which may overlap at least half an octave higher, unless you use a very steep 3rd or 4th order slope crossover), you might want to consider having a custom unit built that combines both a woofer and a subwoofer. Do any Audiogon members out there have experience with such an approach?
