We have an old BPT analogue video intercom system with five video handsets around the house. The old system must be 10 years old and is continually failing. I want to have it upgraded to a new IP video intercom. The problem being the wiring is in the walls and replacing it isn't really an option without making a lot of decorating mess. The existing cable is an 8 core multicore cable including a small gauge coax cable. Any suggestions what we could use ?