After searching the internet, I can't find out what the ethernet plug for the mixer is for. Can you use it to remote control the mixer from a computer? Or what is it for?
You can use the port in V2 software to trigger HiQnet Venue Presets programmed via London Architect and System Architect; the iPad app to directly control the Si Compact is still in BETA test so it's not a 'product' on the web site but you can register for information at http://www.soundcraft.com/apps/visi-remote.aspx.
If you have further questions please use the Soundcraft web site Facebook pages or contact your distributor to make enquiries since Soundcraft do not actively participate and monitor any forums.
Soundcraft-Studer Product Management Team