You should use either B48.11 or B48.22 for the power ground connections. Both pins go to the same ground spot on the intake manifold.
Regarding the signal ground for the F/IC, what exactly is that? Is it just another ground or is it tied to the sensor grounds? It's probably just going to tie into the same ground as the other two, but you may want to confirm that with someone who has installed one or contact AEM.
Regarding the power, you can hook it up to the ECU power. I don't see a reason not to.
What i did for my AEM FIC install i did this. I think...
B48.22 pwr gnd
B48.11 pwr gnd
B48.22 sig gnd
That or i took all the grounds onto on wire. Like B48.22.
I dont think there to much to worry about thar.
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