Wow, this is a lot of great responses - thank you very much, everybody! Unfortunately I can't really make any changes to the front speakers, so putting 9's there isn't really going to work.
As I was planning on getting the sub-woofer anyways, perhaps I'll start with this, as Peter has suggested. It seems like the general consensus appears to be to simply get another pair of Beolab 3's and either wall-mount them / put them on stands or, alternatively, as Peter has suggested above to get a pair of Beolab 6000. Interesting that nobody seems to advocate 8000's ... I wonder why!
Thanks again for all the responses - some really great info here!