Ok, so this Jim Parsons idea seems a bit off to me. I fear he would look too awkward and out-of-place for a rock musical. So many people see him only as Sheldon Cooper, and, from what I've seen of his work outside The Big Bang Theory, he's either too similar to Cooper on a personal level or relies too heavily on the "schtick" he's developed with that particular role to really make other characters believable.
Jeremy Renner seems like a pretty cool choice. Casting P!nk as Yitzhak (with an unknown as Hedwig) wouldn't be a bad idea, either.
Every living soul has got a voice - you've got to give it room and let it sing.