....Third, to my knowledge NJT uses a different voltage on at least some of their lines. I'm not sure about the AEM-7's, but I know that the Acela power cars cannot draw power from NJT's Morris & Essex line, and most likely that means that the HHP-8's can't either. I'm not sure what voltage the Raritan line operates on, but then I'm also not aware of any wye's out that line that would be convienent. It would be too far to ferry the trains to the Long Beach line, and again I'm still not sure of the volatages there, much less the presence of a wye near the corridor.
I believe NJT uses the standard PRR 11kV , 25hz for the old PRR lines or 25kV, 60hz for the modern electrification (same as Amtrak east of New Haven). Either power set up is compatible with Acela. Of course, that is pure academic. There is no need to wye an Acela set and, as you stated, the operational complications make any use of NJT trackage impractical.
I'm not sure what voltage the M & E uses, but I was told that it was incompatible with Acela's power cars. I know that during one of the old Try Transit fairs that NJT used to hold in Hoboken that shortly after Acela's introduction, Amtrak parked a trainset in Hoboken for the weekend for people to tour.
Said trainset was hooked to 480 power out of the station and the pants were down. The trainset had to be towed in and out of the station. Now I can't promise that it was power issues, but that is what I was told, that they couldn't handle the voltage on that line.