I have two of these engines and they came stock with literally booming sounds (as well as huge smoke output) - as good as any Lionel steamers with speakers only in the tender. Bear in mind that videos can be deceptive in terms of sound and smoke output.
I vaguely remember that there was a generation of Legacy engines that had slightly muted sounds. These early Legacy engines were not among them.
I’d check your sound settings; if you can post a video that will help assess whether your sounds are really below par.