If you know anything about Koine Greek textbooks, then you'll know that Buth's method is far from traditional. The method for learning Greek today typically does not place emphasis on being able to understand spoken Greek. This missing emphasis on audio, however, doesn't seem to concern many. After all, the goal is to be able to read the New Testament in Greek, not hear it... right?
Wrong.
http://blog.pricelesseternity.com/2013/01/book-review-living-koine-greek-part-one.html
http://www.biblicallanguagecenter.com/
https://danielstreett.wordpress.com/
https://danielstreett.wordpress.com/2013/02/11/an-interview-about-greek-pedagogy/