VivienM, a second IP would definitely work. Or, technically, a second internet connection, which is would I would be getting, and is what a secondary from Rogers would have been. One connection to the SMC, one to the 891 (well, to the modem and then to the 891, technically.) Your'e right, though, that with the SMC that may not be possible, but I've been with other cable companies before (when I was in the US) where the devices they used were more than capable of dealing with two public facing IPs and splitting them once they were inside to two different neworks.
Plus, the 891 is a router, so I wouldn't need to build a device with 3 NICs in it (although I do have something like that here, it's currently in use as somethign else and cannot be repurposed.)
Datalink, I am unable to access the outside. Just both sides (external and internal) of the SMC.