Not only he changes his expression, but also, he changes his voice when he plays a role.
こんにちは!
ご質問ありがとうございます。
『(俳優さんが)表情だけでなく声まで演技してる』は、
Not only he changes his expression, but also, he changes his voice when he plays a role. と表現できます。
『彼は演じる際に表情だけでなく声まで演技しているところが好きだ』は、
I like him because not only he changes his expression, but also, he changes his voice when he plays a role.
と言えますね!
メモ
not only A but also B AだけでなくBも、AのみならずBも、AばかりでなくBも
play a role 役割を果たす、役を演じる
参考になれば幸いです。