That sounds perfect, as for the audio, the speakers will be directly connected to the HU where the DVD will be playing from so that's where the sound comes from.
The picture will just come from the video output on the HU and into the input on the satnav so all should be well!
Thanks for the info guys, just emailed caraudiosecurity to see if they can get the one I showed you on eBay or similar as well as the adapter to make the Bose speakers work properly and the steering controls.
Thanks again!