There are two things going on here: your criminal case and the civil demand. As far as the criminal part of it, you absolutely need an attorney. You're likely going to be charged with petty theft, and a conviction will have lasting negative implications. You're attorney will possibly be able to get the charge dismissed or reduced to an infraction. If you can't afford to hire a private defense attorney, you can request a public defender at your arraignment.
As far as the civil demand, you can...
If the other driver has an attorney, the attorney will most likely make a demand with your insurer. Your insurer has a duty to settle if liability is undisputed. However, because the unsecured speakers caused the injuries, your insurer may decide to not fully compensate the driver for his injuries. That is, your insurer may decide that the driver's injuries are partly his/her fault for not securing the speakers.
In any event, if the driver sues you, your insurer will hire an attorney to...
The employer is not the one that presses charges. The prosecutor will decide whether or not to file theft charges. You'll know when you receive a summons. Like the attorneys said, these things can take time. You should already be speaking with a criminal defense attorney about this. In the event that you are arraigned and you cannot to hire a private attorney, you'll be able to request a public defender. Good luck.
Call the clerk and ask for an extension. They are usually pretty liberal with extensions if you tell them you are unavailable that day. You'll still be eligible for traffic school. The judge has discretion to lower the fine.
I don't suggest dealing with the insurer on your own. Although it sounds like you have a pretty good case, I can almost but guarantee that the insurer will offer you some nuisance fee to make you go away. Don't accept whatever offer they make. Also, I hope you didn't send them the only piece of evidence you had.
If you have any question, I'd be happy to speak with you at no cost. I handle these matter frequently.
Law Office of Steve Leydiker
Depending on the complexity of your case, you could use Judicial Council form DISC-001 for your general form interrogatories. This is good to use in the beginning phase of discovery. You can find a lot of what you need here: