"she has been running off and having sex with black males that are aka ghetto gangsters..."
I'm uncertain as to why you felt the need to mention race in your story. Would you be happier if your 17 year old daughter was having sex with (several) white, asian, or latino guys?
Promiscuity is promiscuity regardless of the race or income level of the men/boys your daughter is having sex with.
You need to get the police involved concerning any death threats.
If your daughter is aligned with the "ghetto gangsters" then she has already made her choice. You can move to have her emancipated or removed from your home.
As you mentioned you do have other children to look out for.
Therapy only helps when the person going to the sessions wants to change. I'm fairly certain the problems you're having with your daughter did not suddenly appear (overnight).
Somewhere along the line you lost your grip on your daughter.
You may benefit by going into therapy yourself as well as gaining additional parenting skills to prevent your boys from following in your daughter's footsteps.
Unfortunately discipline, respect, and obedience are no longer traits parents' value when it comes to raising children in this day and age. Parents introduce their 5 year olds to adults encouraging the child to address them by their first name!
In past generations kids were taught to address adults as Mr./Ms.
When children believe they are (equal to adults) it creates a slippery slope when it comes time to enforce rules. You may want to contact your local chapter of “Tough love” for advice. http://toughlove.com/html/corporate.php
The key to any happy marriage is having both people in the marriage wanting the same things. Your husband has given up on your daughter and you have not. Everyone is entitled to have their own "deal breakers".
Best of luck!