A suit is an interesting thing.
If you have to wear it, it can really suck. However, if you can get by without it and CHOOSE to wear it, suits are the bees knees. I would like to upgrade my business attire, but the fact is that I work in an office where I occasionally have to load a truck, receive a shipment, crawl under a desk, help schlep a server, etc. I would trash a suit in short order. I am tough on even casual clothes.
That said- the guy said it wasn't open for discussion, so just don't discuss it. Show up Sunday in your nice suit, polished shoes, just minus the tie and see what happens. If the choir director/ pastor makes an issue out of it or benches you for failure to adher to the dress code, clearly that's not the place for you to be. Move on- you're not going to force the issue with any amount of success. If they are that set in their old/traditional ways (again, it's a church) you aren't going to change their minds.