@jhm - sorry, my post was rather misleading. I have an FB2500 which acts as a standby / backup against lightning damage. (The FB2500 was indeed called in from retirement to report for duty a while ago when a port on my FB2700 got zapped. Then AA simply gave me a free, newFB2700 as a replacement, so I didn’t even need to claim on insurance. Even restarted the clock on the warranty I think, iirc. Incredible.)
I have four modems going into a small ZyXEL switch acting as a VLAN MUX/de-MUX, the MUX being needed because there are not enough free ports on the Firebrick. Distinct VLAN tag numbers are associated with each line, which The Brick understands.