When describing a situation where only positive feedback was received, which one is correct:
To my ears Nr 1. sounds more natural, but as "feedback" is being described the adjective form of Nr 2. makes more sense.
In 1. the adverb resoundingly intensifies the adjective positive. It is as if saying:
We received VERY positive feedback.
If you have a look at Cambridge's entry on intensifiers, this may become more clear to you.
In 2. the adjective resounding is in symmetry with the adjective positive, both describing the noun feedback. As if saying:
We received feedback which was resounding (loud, emphatic) and positive.
So yes, you are expressing two different meanings with your two examples.
I don't think it makes any difference to the meaning which syntactic structure you use. Regardless of which "part of speech" you assign to resounding, resoundingly, semantically they're both just "intensifiers". And here's a usage chart for essentially the same construction...
...showing that both versions are about equally likely. It's quite true that syntactically we can distinguish between...
1: Adverbial resoundingly modifies negative - the combination modifies answer
and
2: Adjectival resounding modifies the compound noun negative answer.
...but I can't believe any significant number of competent native speakers would distinguish two different meanings there and choose their words accordingly. It really is just a stylistic choice.
