Andy,
Manual now downloaded. 134 pages to read through then I should hopefully understand this bit of kit.
Post your next image here with all relevant details including lens to subject distance, and we will try to be of assistance.
If you are using the SB600 as the trigger that distance could be important. Too close and most of the flash output from it will hit the background which is fine if you realize that at the time and its what you want.
Does your kit include the Speedlight Commander ?
Don