Second option, setting DNS on the Airport Extreme (5th gen). Noted in the instructions that it needed to be in DHCP/NAT mode, thus the main router in the house.
As we've had fiber since the day it was available my Pace's firmware didn't have bridging so installed the new firmware with it followed by factory reset.
Then read on Geekzone that general expectation was that because the airport didn't have Vlan tagging on its wan port (?) performance would be crap if it worked at all.
Long story short, didn't have any expectation of success, but..bridged the Pace, set Airport to PPoE and Nat/DHCP server, rebooted all, and its working like a champ.
Haven't noticed a single problem, fingers crossed.