Fishing Wire From Corner of Attic?
If you were to attach something similar to the end of the wire such as a hex nut that would not easily slip off then you could make up a remote noose on the end of a long stick that looks like this. 


(proverbial back of envelope sketch)

Aim the stick down into the tight corner of the attic and lower the noose over the end of the wire with the hex nut. Then securely pull the noose string to capture the wire and pull the stick toward you along with the speaker wire.