Not to rain on this parade but it takes a LOT of knowhow to do what you are attempting. Vandersteen has refined the 2's design over some 28 years. I for one would not second guess him in this area.
If the speaker was previously modified, I would try and bring it back to the original design.
When you start dealing with a time and phase speaker, the 6db slope is just the beginning. The drivers are used over a much wider frequency spectrum than steeper slopes and does require custom drivers. Vandersteen modifies his or has them built to his specifications to serve the intended purpose. The 6db design is probably the hardest to modify because of this.
After all of that, then you must deal with the phase characteristic of any driver used. Correction is then applied to bring phase relationships into line using those selected drivers. Each one is individually tested in all parameters. This is one of the reasons the drivers cost more from him because they are a known quantity.
What you are attempting is a re-engineering of the design. Unless I had vast experience, I would leave it alone. Vandersteen didn't get where he is at with hit and miss engineering. He is one of the more knowledgable individuals in the industry and his designs are extremely sophisticated. His bass loading using an 8" driver in a sealed encloseure and the 10" radiator in the rear are unique. The system acts sealed and passive because the "Acoustic coupler" in the rear is also actively driven below 35hz. It is not truly passive. This "System" is pretty remarkable in the world of speaker engineering and speaks highly of Vandersteen's knowledge.
If you mess with the 8", then you have to also deal with the 10". What I'm saying is it is MUCH to complicated for a novice and I wish you the best of luck.
