Can you add the Centrois 8" Passive Subwoofer to the list? These subwoofers have been around for a couple of years and they go a good job with adding in that lower register with bookshelf speakers. I have them hooked up in parallel with my Mission 700s and they blend in quite nicely.

Manufacturer Name: Centrios
Manufacturer's Website: http://orbyxelectronics.com/
Category: Subwoofers
Product Name or Model Number: 8" Passive Subwoofer 4018179/4018181
Driver: 8", single coil, rubber surround
Impedance: 8 ohms
Power Handling (RMS) 20 - 100 watts
Frequency Response: 25 - 180 Hz
Demensions: 10"x12"x14"
Price: $79.99 CAD