Use either the SB800 or SB900 on-camera and place the diffuser dome on it. This will spread the emitted light to both sides, possibly enough to fire the remote unit(s) reliably. Yes, this shorts you one remote, and may cost you a little in total power reaching the subject from the on-camera unit. You were looking for a reason to acquire another CLS compatible speedlight anyway, weren't you?
As others have pointed out, make sure the small IR window on the remote unit(s) face the camera.
HBB in Phoenix, Arizona Nikonian Team Member
Photography is a journey with no conceivable destination.