ProtegeManiac
Headphoneus Supremus
I'd asked around elsewhere as well, and it appears that you get all 4 DACs and/or "pipelines" regardless of the mode.
See here. Very awesome news!!
BTW if you root the phone you can just enable high impedance mode all the time. Won't be great for battery life but, well, this is Head-Fi. That was only really a problem back when the DAPs that started the post-iPod era wouldn't last all day and we didn't have powerbanks. Given how thin phones are and you could lug around a powerbank or put it in a battery case, anything short of forcing a portable unit to run in Class A (like some rollable op-amp DAC-HPamps) wouldn't really have a problem.