We have a customer with 55 locations and only one of them has a DX80 installed. They've had all kinds of problems with it over the years to the extent that we've replaced the KSU. They are on the fence about keeping it.

They have asked if we can add two door boxes to this system. The current system has 16 digital phones on it and that's about all that I know. What I need to know is:

1. Did they even make a door box for this system?

2. If they did, is there a chance of even being able to get them these days?

3. If they did exist, how do they connect to the system? Digital station ports? Dedicated ports for door boxes?

4. If they are available and can be connected, is it possible for them to ring all phones in the system?

Thanks in advance for any input you can provide.