Edgeport 8 and Modems

We’ve installed new servers using Edgeport 8. 6 Multitech modems are plugged into the device on COM3-COM8. Communication to the modems fails on all but one of the ports. Before attempting installation, I tested a multitech modem on COM3 and it worked. When we plugged in all 6 modems only COM4 worked. We’re not getting any errors in windows or anything - the modems just don’t ‘see’ the server. We know the modems are good because they’re currently working on a Digi PCI board.