holmz,
Points well taken. I really like your idea of an active crossover though. I have done it in the past, but not with quite as good results as I would have liked. The development was by engineer friend of mine who set the frequencies and slopes, etc.
The cabinet is a model DNA2 by Decware Audio that I built a couple of years ago. It stands about 39" high X 10" wide X 17" deep. I'm kinda guessing here, but that is in the ballpark. The claims to frequency response by Decware are nearly realized, but I bet not down to the 20hz claimed. Seems like there was a bump at 40hz IIRC.
The drivers are 18WU/8741T, which is a 7" midwoofer with a neodymium magnet.
FWIW, I have just received an email from the customer who has access to crossover information/design that will solve half of the problem. He will likely use passive for the design, but I will mention the electronic crossover idea anyway. Glad that you mentioned it.
The cabinet may seem large, but actual area for a passive crossover would be right in the space behind the woofer. Not ideal if you ask me. I would rather run more wire and two more binding posts, and have a biamp situation. That way, I could go either way with a crossover.
Thanks for helping me think this through. I'll sleep on it.