You better understand your speaker before you "do things to it " !
A couple of drivers on it are passive radiators ( ABR's) which are more floppy than the other drivers and have no voice coil . I'm assuming you have the same speaker being talked about here. The real bass driver with a voice coil is the third from the top ( according a Youtube video!). The other two ,above and below the middle 8 inch bass driver ,must be ABR's ( no voice coil ). No point removing the ABR's unless you need to do that to access the crossover if it is located behind them.
" All the drivers, including the tweeter, have aluminum domes with the top Uni-Q driver having an interesting ribbed surround. Of the three bottom 8" woofers, only one is powered with the other two being passive radiators (or what KEF calls Auxiliary Bass Radiators). This allows the Q900s to forgo the usual port while still maintaining a bass reflex design. "
( taken from :
KEF Q900 Floorstanding Speaker Video Review | Audioholics )
Might be very helpful if you do a full fledged search on the Net . I paid Mission about Rs 6000/- for 2 small 5 inch drivers a few years ago ( without shipping). 10K for a new (imported) 8 inch driver plus labour sounds very low.
Better you check things out with help from the Net.
Contact KEF and explain your problem " very clearly ". See what they have to say. Unless it is a standard problem it might be hard for them to actually give you a perfect solution without seeing your speaker.
http://www.kef.com ( just go to support or 'contact' them )
Ask them for the circuit diagram of the crossover.
This should be your first step . Meantime collect more info from the Net.
Don't rush into the repair. If you don't know what you are doing , you could screw it up. So learn it up from the Net and people who can help. It 'could be' something simple.
Note that the bass driver will move excessively if played outside the box ( in open air). This is normal. The ABR's shouldn't move at all if the bass driver is removed from the cabinet. Keep the volume down to avoid physical damage.
I just noticed that you have a pair of screw in 'connectors' at the back for bi-wiring. When screwed in, it connects the UniQ driver and the bass driver together. So surely the top driver has it's own enclosure.
Now if for some reason the black screw tops have been unscrewed the two drivers could be disconnected. Might be a good idea to put it in bi-wire mode ( unscrew the black connectors ) and connect the amp to each pair of terminals separately and confirm the separate drivers work or not. If you have removed the 8 inch bass driver already , you can connect any 1.5 volt battery ( it's safe ) to it's terminals and see if the cone moves in or out ( it will move only in one direction). Might be a good idea to disconnect the bass driver from the crossover by removing at least one terminal connection. It should move , otherwise it means there is some problem with that driver.
