Have you seen these?
7" x 10" 3-Way Speaker
If size permits, the 320-watt, 7" x 10" three-way KFC-X718 is the speaker to select with its huge 18 oz magnet on the back of the silver PBO (high-performance) fiber woofer cone. The midrange driver uses a 2-3/4" PEI (Poly-Ether Imide) poly-film cone and the 1" dome tweeter is also the PEI type for exceptional response and excellent power handling.
Recommended Price $300.00
- Designed to Fit Many 6" x 9" Cutouts Providing 30% More Cone Area
- Frequency Response: 22Hz - 33kHz
- Impedance: 4 ohms
- Magnet Weight: 18 oz
- Multiple Component Crossover Network: Outboard
- Power Handling: 320 Watts
- Rubber Surround
- Sensitivity: 93dB
- Speaker Connectors: Gold-Plated
- Midrange: 2-3/4" PEI Film Cone
- Tweeter: 1" PEI Film Banalced Dome
- Woofer: 7" x 10" Silver PBO Advanced Fiber Cone
I used to sell these many years ago and they were pretty impressive back then. They are basically a 6x9 but larger, they come with an adaptor ring to let you fit them into 6x9 openings in cars. But for a tower application I would think they would be one of your best options. As stated above the ways to make it louder are more surface area and more power. Here is a way to improve on one.
here is a link to the website I took the above info from: http://www.kenwoodusa.com/product/product.jsp?productTypeId=43&sortBy=price&productI d=735