"Inaudible" is an adjective, and it does not seem to modify, describe, identify or quantify anything in your sentence. Furthermore, an adjective usually precedes the noun or the pronoun which it modifies.
I think you need to rephrase your sentence. I understand what you are trying to say, but you are not expressing it grammatically.
Can I say, 'You are (being) almost inaudible' when I really can't hear a man who I am talking with? Is the part in brackets mandatory?
"You are almost inaudible" sounds fine to me. "You" stands for the noun "your voice". (Just at the moment, I can't think of the literary term for using the whole to mean a part; but the sentence is legitimate, and grammatical to me).
No, "being" should not go there.
PS: If you're talking on the internet or a phone, etc. and reception is not good, you can also say things like "You're breaking up", which is not to be taken literally.
So what if I replaced the adjective inaudible with the inaudibly adverb?
I have learned from the OALD examples that I can say, 'Your voice is almost inaudible' but it sounds to my ears a little abundant (can I say that?).
So I just want to figure our can that example can be reduced to a simpler form.
P.S. Raymott's point seems sensible to me as well. So what would we do about these two versions ?
"Your voice is almost inaudible" is a perfect sentence. It clearly and succinctly explains exactly what you want to say.
"...but it sounds to my ears a little abundant (can I say that?) No, abundant isn't the word you are looking for.
Redundant means no longer needed or useful; superfluous, but I'm not certain that is what you wish to say either because "inaudible" means "unheard" and "almost unheard" is not redundant.
Thanks. Hmm, strange that the two opposite concepts should have the same name.
Another example would be "England play(s) Australia tomorrow at Lords", in which "England" and "Australia" refer to their respective cricket teams. I thought there was a more specific term for that.