To write a single DSK image file you can either use :
Beware, WriteDSK works on the CPC (you must have a PC 3,5" with the .DSK which will be copied on the same 3,5" drive or another 3" drive). It supports the CPC Booster by Antitec.
But if you want to write a double sided DSK, you will have to use CPCDiskXP by Mochilote for the moment.
P.S. : from the WriteDSK documentation, it should support double side DSK.
Source : CPC Wiki's forum