I would just keep the speakers in it for now, because it is not really worth upgrading the sytem from bose unless you do the whole shabang. bose is heavy on midranges and reproduces them very well that is why evryone thinks they are awesome (because are hearing is most sensitive in midrange area). highs and lows are reproduced well/ok also, so they are well rounded speakers. Where if you buy aftermarket speakers, they play no lows so there is no fill in that area unless you add a sub. It won't sound bad by any means if you replace the speakers, but it really isn't comparable since they play different frequencies.
Long story short, keep the bose for now.
good choice on the 9883, it is an awesome unit. I have the 9885 (only diff is the display it isnt the dot matrix, its the bio-lite) right now in my car, until the alpine w210 double din comes out.
