We have the Polycomm Sound Station 2 on our BCM400. The Sound Station 2 appears to have its own ATA built into the power supply. The unit shows up as a 7100 on Element Manager.

Is it possible to have more than 2 outside callers on a conference with this unit? If not, are there other units that allow more than two outside parties on a conference call?

If it sees the unit as a 7100 then it is a Digital Polycom. ( It does have a FEATURE key on it ???? )

Your older software can only do a total of 3 parties on a Conference call. Yourself plus 2.
Newer software would allow for more.

I do not know if this is phone dependant or not, but once you make a normal conference call and have yourself plus two more, then try hitting FEATURE 807. If you have the right phone/latest software then you can add more people. I just don't know if you must have a two line display phone to use this feature.