@hayden88,
Hayden, I am so sorry. 10 years is a long time and they still won't accept "who you are" . I don't know if a letter will help, if they are set in their ways nothing and I mean nothing will change their "old fashioned ways" but it will help you, you've written it, sent it, expressed.
There really isn't anything else you can do.
The thing is you are your own person. Parents give birth to us but we choose our paths in life.
It may be that they don't accept who you are but I want you to know that, that is "their problem" please do not allow it to bring you down. You have a lovely wife who I can only imagine you love and a family.. Focus on the positives not the negativesw.
As for where you want to go, you already know they couldn't see that in their mind. At some point in our lives - we do all come together.
Tell them you love who you are and you are proud of they way they bought you up after all as a result you choose to be yourself and not a sheep, a follower and you are grateful.
Sometimes hearing that they did good despite their own opinions of life can move.
Ultimately though be happy don't let it affect your relationship of that of your wife and family...