Yep, Steve's spot on, the off command switched all channels on the Graffik Eye
If the cost of two units is getting too high then why not look at the iLight Zen as an alternitive. I've not priced them myself but have heard from a number of sources that it is priced to undercut the Graffik Eye and so could go some way towards helping with the problem.
Other possible alternitives could be the new Leax Scenemaster 4, a 4 channel dimmer that fits a double back box. Total circuit load is 2kW and the units can be networked.
Mode are also about to launch something similar so it may be worth waiting a week or 2 to see what develops.