I have the setup you are talking about. BV 7-40 with 7.4 and BL 9 plus BL 2.
My point of view: First I had the BL 1. Switching to BL 9 gave a whole new world of meaning. They play even more detailed, and they pack a punch that the 1's, and the 8000's I have heard are no where near.
When I listen to music I put on speaker 2, leaving the 7.4 unemployed. The sound is really much better when you let the 9 play the major part. Also, even if the 2 is connected, it is barely noticable when playing music. The system doesn't really allow it to enter somehow, if you catch what I mean?
Movies are an entire different story all together. Even with the 9's I have had significant enhancement of the soundpicture since setting up the BL 2. The detail, and quite a punch, is delivered fine by the 7.4 and the 9's. However the BL 2 has added the last ten percent of perfection as rumbling action scenes, or just plain traffic for that matter, takes the stage.
My recommandation is clear: Ditch the 8000's but keep the BL 2. It will provide the best of both worlds. However, if selling the BL 2 is part of the financial plan to achieve the BL 9 I say go ahead and do it. All together I think you will be better off than your current setup.
I can not even begin to tell you where you will be at when you let the BL 9 fill your house with the music you love the most. The Beolab 9 is exceeded by one pair of speakers only - sadly out of range for me. At least for the time being.
Good luck in your decisionmaking!
BV 7-55, BL 7-4, BL 9's, BL 4's, BL 3's, BC 2300, Beo5, Beo4