to both ears vs in both ears

to both ears and in both ears both are adverbs.

Word	Noun	Adjective	Verb	Adverb
to both ears	No	No	No	Yes
in both ears	No	No	No	Yes

As adverbs, to both ears and in both ears are synonyms defined as:

Other synonyms of to both ears include binaurally.

to both ears (adverb)	in both ears (adverb)
in a binaural manner	in a binaural manner