I have extensive experience with the Avaya conferencing products. Here is the basic rundown.
Meet-Me conferencing provides 6 party conferencing on the PBX with no bells and whistles.
IP Office can provide basic conferencing capabilities as a back end to Communicaiton Manager with up to 128 ports.
Expanded Meet-Me Conferencing is an external platform that extends the number of parties up to 300.
Meeting Exchange (MX) is the top end product. There are actually multiple servers associated with MX. The S6200 stand alone supports 240 ports. When used in combination with the S6800 it scales into the thousands.
The base unit it eh MX Bridge which provides the conferencing capabilities. We use the SIP integration directly to CM (does not require SIP Enablement Server). With the base unit and the BridgeTalk application (sort of an operator console for the bridge) you can run conferences including recording.
The second unit is the Conferencing Reservation Scheduler (CRS). This application provides a much cleaner conference sheduling solution plus you can run the Audio Console which is a web based application allowing end users to not only see the conference (and yes you can get caller id) but also control the conference (such as mute, lecture mode, record). Conferences can also be scheduled from the web server by the end users. The CRS Front End application is a great desktop application for conference scheduling and also let's you review the schedule.
The third component available is the Web Conferencing Server which provides the capability for single party video using the Java Media Framework (JMF 2.1.1), discussion/chat, white boarding, and desktop/application sharing.
Just released is the Avaya Video Telephony Solution (AVTS) R5.0 based on the S6800 (I believe this is OEM from Convedia) in conjuction with the MX Bridge to provide a video conferencing platform. Capabilities include both scheduled and adhoc conferencing (with CM5.0). The adhoc conferencing allows a two party direct conference call to add in a third user and migrate onto the bridge.
What's nice about this whole package is that it is also being integrated with the Avaya one-X Communicator.
We are a VAR and run conferences constantly and this has been a very stable cost effective platform for us.
I did a little slide presentation in 2006. See attached URL.
Jimbo