Last time we set that up, we used a Dee's service observing unit, hooked to a single line extension, and accessed that extension from a DISA. Of course in a situation like that, you're monitoring the trunks, not the extensions. It's been several years, so I'm a little foggy on how we hooked it up. It was actually on a Premier as I recall, but it's something to think about if it'd work for what you need. Sounds like you really need to be able to monitor stations, not trunks though.