asking this question

If I want to ask this question to someone:

If you had to change your position in the band, what position would you choose?

- As in talking about a band they are in, and wondering what they would do if they had to play a different instrument than they do now.

I have no idea how to put together this sentence, I first thought "何を選びますか？" for the last part, but I want to clarify the question a bit more..

The question to ask would be "もしほかの楽器（がっき）を選択（せんたく）できるなら(or するなら)、どれを選びますか?"

JenJen89,

もしも（同じバンドで）パートを変えるとしたら何を担当したいですか？

Moshimo (onaji bando de) paato o kaerutoshitara nani o tantou shitai desuka?

- Please omit ( ) contents if you don't mean "within the same band." Also, I'm assuming you don't necessarily mean "instrument," because you're supposed to have the option to become a singer.