As a husband with ADD here's my response: a wife should make the perfect coach, mainly because she is available all the time, when coaching is really needed.
But more importantly, I've looked at your words and question them:
"because having ME help him with the tasks he finds difficult always results in fights and tears. I'd rather be taken out of the equation, but I don't want him to be left to fend for himself when clearly he struggles with things he NEEDS to be responsible for."
1-always results in fights and tears...then are you really helping him?
2-you'd rather be taken out of the equation (not involved) so are you doing this relutcantly, maybe with resentment?
3-the capital NEEDS seem more like your words than his.
Maybe the two of you have different definitions of what 1)he wants you to help him with
2)you'd rather not help him with
Once you define those areas the coach position will have a better chance of working.
Please let me know how things work out!