I tried this out last night but could not get it to work. When I bought my D90 I went ahead and bought an SB-600 to go along with it. Well I didn't want to just throw my Vivitar 285HV and cactus triggers in the junk drawer so I tried sticking the transmitter on the D90 and using the commander mode. When I did this only the Vivitar would fire. I think the problem might be you have to have the onboard flash raised for commander mode to work, and when you put the cactus trigger on at the same time it pushes the onboard flash down just a bit, which might be making the camera think it isn't raised at all so it fire the shoe only? I would like to have 2 remote flashes without having to buy another SB-600, but if the cactus can't be used at the same time as commander mode I guess that will be my only option.