I had 5 9.0's (7 if you count the column 9.0's) and it made a killer system.
The ceramic 4.0's were very nice as rear surrounds when I tried them for a short period.
If you can fit a third 9.0, mini or otherwise as a center, go for it, if not, then the ceramic or marble 4.0's match up pretty well.
As far as subs go, there are almost to many to recomend. What's your budget for subs, and do you like box or sonotube?