Improve input audio signals to car audio system
You don't need any resistors.  If provided with the correct voltage, an appliance will draw as much current as it needs.  So long as the power supply can supply that current, all is good.

As for fuses, you'd have to check your power supply.  Many have built-in over-current protection, and will simply shut down if the output is shorted.  If yours doesn't, then an appropriately rated quick-blow fuse would be a good idea.  But you'd only need one, to protect the power supply.