The Accutrons that I've heard really are quite good drivers in the right application- just incredibly expensive. I really think that you are doing this backward, but if you are going to do this, here is what is needed:
1. Design goals. Full range (tough to do with that size woofer in sealed bass)? Supplement with sub? Priorities for mids (fingernails on blackboard clarity to soft to the point of muddy) Do you want to keep that tweeter? (it's good, but obviously there are better but they may not fit the hole)
2. Budget
3. Do you want to do it all yourself, what is your skill level? Have you ever designed speakers before? Do you have tools? The woofer holes are cut for a surface mount woofer, most of your options will have to be recessed- you will need a router, bits, and a circle jig.
4. Do you have access to calibrated measuring equipment? Without it, you can't really tell what is happening.
Good luck with you project.
Thats more like it

1. Design goals. Full range (tough to do with that size woofer in sealed bass)? Supplement with sub? Priorities for mids (fingernails on blackboard clarity to soft to the point of muddy) Do you want to keep that tweeter? (it's good, but obviously there are better but they may not fit the hole)
1=> I have stereo NHT U2 setup with two 12" aluminum in sealed enclosure with external amps. They are not connected to the system at the moment. The current extension is flat down to 60hz and I am satisfied with it. So 60hz to 20khz will do
Bass: Need powerful bass not necessarily the extension but amplitude
Midrange: gotta be soft but not to the point of muddy (Rock music recordings are usually pretty bad, less listening fatigue is better)
Tweeter: Not married to the existing one even though its pretty good. Again less congested is better considering the style of music I play
2. Budget
2=>I wanted to buy Sonus Faber Luito ~$6000 (new) minus $1200 I spent so far on the X-Statik + amp + calibration setup so $4800 to play.
3. Do you want to do it all yourself, what is your skill level? Have you ever designed speakers before? Do you have tools? The woofer holes are cut for a surface mount woofer, most of your options will have to be recessed- you will need a router, bits, and a circle jig.
3=>I cannot do wood work, no space and no skill. Rest I can handle easily, I work on my cars myself so pretty handy. Can only do electric and electronics. This is where I need your help. I need the drivers that can fit perfectly in the existing space...
4. Do you have access to calibrated measuring equipment? Without it, you can't really tell what is happening.
Good luck with you project.
4=> I have a calibrated mic. good USB external sound card running variety of software from RoomEQ wizard to Holm Impulse. I can buy more if so recommended.