Yes, one such consideration is the touchscreen beeps routed through the audio system, even when the radio is off. By the way, those beeps reportedly get amplified to an obnoxious level when an amp is added - something else the PAC-OEM2 can apparently fix using its output adjustments.
Fortunately, it seems the beeps (and hopefully everything else) on the STANDARD Prius audio (but not on the premium) are routed ONLY through the front channels. That being the case, I'm hoping hooking up the PAC's sensing wire to one of the rear speaker wires will solve that issue.
Also, wouldn't the alternative be an even bigger risk for the problem you mentioned: hooking up the amp's remote line to a 12v acc in the car would mean the amp would ALWAYS be on anytime the car is on, dramatically increasing I'd think the likelihood the amp will be on without the radio on.
The risk the amp will burn up under that circumstance is of course important to me but also how much electricity is used up by the amp when no signal is sent to it (radio off). It'll be the aux battery on the Prius that will power the amp. It only supplies 80 amps total.
These are the grounding / reliability issues brought up and the threads where:
"... however this may introduce a ground-loop if you ground the line-level convertor at a different potential than the headunit. If you put the line-level convertor at the back and it requires a ground, you should also run a ground wire to the deck instead of grounding it at the back with the amps."
(Not sure what was meant by the last sentence as I had no intention of grounding the deck anywhere other than it was at the factory.)
https://www.the12volt.com/installbay/forum_posts.asp?tid=53306&PN=2
"I don't like trigger devices that sense signal in OEM speaker wires, and I don't like to ground a device that's a part of the signal path if I have an alternative. So if it were me, I would run a remote wire to the amp from a switched power source. That wire would be fused (1 amp fuse) close to the power source. The amp will be on when the car is on, off when it is off. The LOC will act like an LOC and not be depended upon to trigger on the amp. And you will have one less ground plane....because as you know....or will know by this weekend if you study BCAE1.com....ground planes are the primary reason for noise."
https://www.the12volt.com/installbay/forum_posts.asp?tid=53350&PN=1