We're back, connected once again: some techie must have been in the neighbourhood saturday night, because Saturday 2138 line-sync suddenly reappeared, and today I finished setting up the remaining bits (e.g. inbound POTS-to-VOIP etc.) and verified that Internode didn't make a mess of their part of the service conversion.
Looks all mostly good, except line attenuation has jumped up 10dB (without the previously required inline filter), which makes little sense, and sits now at 50dB downstream. This sucks as it severly limits the achievable sync speeds and makes things a tad more brittle. Ticket open, we'll see.