It is difficult to understand what it means.
Many of the themes just sounded have been confirmed and amplified in more recent work.
I suspected it could be replaced by "just mentioned" but I don't remember having seen "sound" used in that sense. So the alternative that comes to my mind interprets "have been..." as the other predicate of the subject and renders "sound" in its usual sense of "appear" or "seem" which means the sentence can just as well be rewritten as this:
It just sounded that many of the themes have been confirmed and amplified in more recent work.
But with this interpretation the original sentence still "sounds" awkward to me or I may be wrong. Help appreciated.