A 9 DOF sensor has three sensors: gyro, accelerometer, magnetometer, each with all three axes sensing.
On the cheaper ones, you actually just get the three chips and have to talk to each one yourself.
In your case, if you only need to worry about 5 axes, you could just ignore the magnetometer, and ignore one of the axes from one of the other chips, to get the same kind of input as you'd get from a 5 DOF sensor based on accelerometer and gyro (I'm assuming that's what it is -- specifying this clearly would help.)