Dimming multiple power LEDs with individual constant current PSUs from a single arduino?
I really do not think it is possible to regulate the output of the fixed CC driver due to the fact that it will be continually tracking the output current and trying to keep it at 320mA and varying the voltage to do so. 

To be able to do it I would suggest investing in new drivers that are constant current but accept pwm input, after a quick search I came up with this driver from Amazon or this one from eBay. 

It is very inexpensive and would use a common DC power supply. With the requirement of 5 to 35 V input, with the current set to 350mA x10 would only require a 220AC to 12V@850mA supply, though I would try and find a 1.5A or 2A supply to have some headroom. These drivers appear to directly accept PWM input so no additional circuitry would be necessary for this functionality.