I used to repo cars for Daimler Chrysler. That is to say I approved the repos, didn't actually go out to get the cars.
I can tell you that a voluntary repo is just as bad as any other repo. Here is what will happen.
Either repo you'll be sued for whatever amount is till left owing. They will sell the car at an auction and will take the best offer that day. If you owe 7k and they sell the car for $4k, you're going to be sued for that difference.
Voluntary repo only saves the repo charge of $350.

Talk to the bank and let them know what kind of financial trouble you're in.. tell them you'd like to keep the car and work it out.

Do not do a voluntary repo.. it will ruin your credit and you'll still pay for the car......

Good luck!

CS