Hello Charles,
Thanks for your interest in my loudspeakers. Now is a good time to purchase 15HM drivers, as they are on sale at
www.partsexpress.com for $138.00 and free shipping. These are exactly the same speakers that Usher use in the D2.
However, the D2 is designed to be a high efficiency / low distortion speaker, and its bass extension will NOT be as good as a top of the line subwoofer. Please see the plot below.
The red curve is the 15HM in a 10cf cab tuned at 28 Hz. The other Usher curve is my smaller upper cab tuned to 35 Hz. The JBL curves are for their M9500 with their speakers (1400 Nd) and volumes. These curves are NOT measured, but caluclated with the best T-S parameter data that I could find.
Note that the Usher with the 10cf cab is the best, but not exactly in the subwoofer class. Bottom line, I think that you might miss your subwoofers on your pipe organ and home theatre "earthquake" material.
Good luck with your project.
Linear