Seriously, it never occurred to me that you could choose an appealing voice for your inner monologue, mine has always been a neutral version of my real voice. Stranger since I subvocalize while reading, and as a kid, the voice would actually act and change for each character.
Not the parent, but for me I have to actively remember what the target voice sounds like and consciously alter my internal monologue to match. As soon as I relax this acting process my internal monologue slips back into my neutral voice. So those, "you're now reading this in X's voice," never really do anything for me.
Maybe related, I don't always experience my thoughts via an internal monologue. Maybe roughly 70% of my internal thoughts are abstract and nonverbal.
Can you do an impression of Darth Vader out loud? Just curious, because when I do Darth Vader voice in my head, I get a strong urge to do it out loud. Makes me wonder if they're connected.