Jewish Music Insider: Who Arranged that Album?

I was recently speaking to a musician friend of mine about Jewish Music. We were discussing different aspects of music in general, when he mentioned that the arrangements on The Yeshiva BoysChoir are some of the best he's ever heard. I'm not sure if I'd agree with his sentiment but he brought into question whether Eli Gerstner actually arranged all the music on his own. Perhaps he had a rough idea of what he wanted and he used some unknown arranger to assist with writing all the parts so that they made musical sense and all fit together. He felt that some of the ideas were too advance for someone with no major musical training. It's a good question as to how much of some of these albums are actually arranged by the people who are getting all the credit.