Out of curiosity , I did a search and apparently, this same question was asked earlier at AH and Polk forum.
Question came up elsewhere, as apparently some avr manuals warn against doing such for a given channel(s). If you did utilize both the pre-outs and the speaker terminals for the same channels for some reason, would the reason being advised against doing so be electrical in nature or just a...
forums.audioholics.com
Seems Yamaha manual explicitly discourages such config:
I am looking for thoughts on the following: I am currently running a Yamaha aventage 3010 AVR.
forum.polkaudio.com
With Marantz blowing transistors on the Front amp channels , with a loud pop on Height speaker(Atmos/Ceiling) - which is how I discovered the amp reassignment from pre-outed Front channels to Heights (although that wasnt the cause of transistors blowing), I'dnt try such a non-standard configuration in my system , even if it works , if it was upto me!
Neverthless, in this particular case, I strongly suspect the front amp channels are already accounted for - being redirected to power height channels , unless he frees them up.