ya i know... You cant run 16v thru the entire car. So if you had a HC16v and used one post for the system and one for the car, or a step down module or we the car would still be 12v. Since HU's arent 16v stable and they are wired thru the car harness in 99% of cases the HU is still 12v. Even assuming it was 16v and worked not sure if it would then put 16v on the remote output. So Unless im completely off base the only correct way to get a 16v remote is to wire a relay to the 16v power source.
TO clarify my setup is a second electrical system. Ohio gen with an external regulator at 18.4, 2 HC16v batteries but the remote to my sub amp is off the HU so its not at 16v in any way shape or form.