OK, back home now.
So - EC FX is installed, had a 975 or so mile drive home, only one issue. Had a EngSys amber light come on, with a DPF icon also ambered out. Reason was a very long uphill in 95 degree weather (the Grapevine, heading south, for those of you that know it). I downshifted, three miles later the warning reset, all is well. Topped out at 42mph too, by the way, if anyone cares. (Steinbauer!)
The end story about the faults earlier was that it turned out to be a bad NOx sensor. Fuso replaced all sensors in the exhaust system though, not just the NOx. But seeing as how I've had two of the NOx units replaced in less than 7k miles, I think I'll probably start keeping one on board.
So, TL;DR version, all is well so far.