After many helpful comments here and with further reading on Adire vs.
Dayton subwoofers, I'm now tending towards the Adire Tempest in a
vented enclosure using Adire's plans for the Adire Alignment. This
enclosure offers a good compromise for HT and music listening.
Luckily the enclosure plans are highly detailed, therefore I should be
able to create an optimal enclosure.

I found a subwoofer comparison chart on Adire's website that compared
the Shiva's SPL at 20hz (I think it was at 20hz) to other quality subs
including the Dayton Titanic and the NHT 1259. The Shiva outperformed
all of the subs on the chart which contradicts the results I obtained
using WinISD, however, I'm willing to accept the real world results as
more realistic than those plotted in theory.

Now comes deciding on the amp. Unfortunately, the Tempest has two
8ohm voice coils. My Carver amp is not rated for 4 ohm bridged loads
and running it stereo into 8 ohms would reduce its overall power.
I'm looking into the Rythmic 350 which on paper delivers fairly clean
and well-damped power up to about 370 watts rms. It also has a rumble
filter, frequency crossover settings, and damping settings.

bsguidry