I replaced it with a Motorola MR2600, and it's working great through the router out of the box:
Modem status is also looking pretty good, as I'd expect; they ought to be testing their own equipment working well together without needing much customization. This is a good setup too, in case I need support - they can't give me the runaround ("talk to the modem manufacturer"... "talk to the router manufacturer" - it's the same people
).