Interesting question- and I'll be checking back for answers.

Recently our local Arts and Humanities greatly improved the acoustics in their facility. It too was large, concrete and echoy. A dance or concert there was a lot of work. One could hear in the front rows but it wasn't quite worth the effort otherwise.

They put up good looking buffer panels on the walls that break up the sound- I suspect they sought the advice of an expert.

It seems to me that quilts could have the same effect.