Better late than never, finally here's the rest of the review on the S-OSD board. It got replaced from Goodluckbuy without incident, and I couldn't work out what the original problem should be. However I asked Coyote (Ian) from fpvhub to take a look at the wiring as he made a great video about ground loops. He made a suggestion about removing the grounds from the ESCs going into the Naza, so I've done that as an extra precaution.
The two links I mention in this video for the config software are -
This setup is now going into my new Quanum frame quad, which has been so long in the making, even my friends are starting to think it's vapourwear.