You have a range of options. One driver will light 3 cobs wired in series which is running them pretty hard. You might get away with running 4 cobs wired in series, it's close to the max voltage of the driver (152 volts).
Another option is to run two parallel strings of 3 (or 4) cobs per driver, which will make it easier to control the heat put out by the cobs, and result in a better light spread and greater efficiency in turning electricity into useable light.
Two drivers and 12 (or 16) cobs would do very well in illuminating a ~20 sq. ft. space.