ICE-16 units cannot be connected point-to-point over FireWire for linked directly to USB recording, the sync ports must be used for this.
You can daisy chain multiple ICE-16 units on the same FireWire bus when using a PC/Mac.
The dedicated control panel on Windows or the creation of an aggregate device on OS X will allow you to merge inputs/outputs so they can be used as one device within a DAW setup.