There were some negative comments in the past about the default TTS voice. I wrote some of them.
I did a search for alternative TTS engines. There aren't that many TTS engine which can be used in MRA Next. But i found one which i like.
It is Acapela TTS Engine for Android. The app self is free but you must pay for each voice separate. A few Euro's
Because i'm Dutch, i bought the voice "Daan". This is a good voice.
This voice is a lot louder than the default TTS engine. The volume is more or less the same as Spotify. Besides this. The voice is also less mechanical/robotic.