OK, I did all the mods this week and, because the parts came from different sources, I upgraded in stages. Here are the order of upgrades and my thoughts:
The woofer recommended by PinBits: http://tinyurl.com/cov2wdf
This did increase the bass significantly. IMHO, it was too much without an L-Pad to work out a nice balance between the woofer and backbox speakers, even after removing the capacitor on the backbox speaker.
Pyle Blue Label in the backbox: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=267-078
Sounds was better, but the bass still dominated the sound. You will need to remove the grills on the panel to fit these unless you have the ability to make a spacer. I removed the grills. The only downside to this is the blue color if you have anything other than a BIBLE. It's not bad, though. I'll probably try a different set in the backbox since I need to place an additional order and move the Blues over to S-M.
The amplifier recommended by markmon: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-802
I used the more powerful of the two amplifiers markmon recommended. The reason I chose the more expensive of the two is after reading the reviews of the lower end model, a few people had problems with the crossover not working properly. For placement, I simply put it where the coin box goes, which allowed me to wire it all up without clipping zip ties on the cabinet harness and pulling the wires from the main bundle should I ever (doubtful) choose to remove it.
All I can say is WOW! This really brought the audio to life and with both the volume and crossover adjustments, it allows you to dial the sound to your personal taste. I am very pleased with the results! Thank you, markmon!