Re: Speaker problem
Next I would check fuses (not sure if they are arranged laterally like that, but it wouldn't hurt to check).
Following, I'd look at the relay that controls power to the speakers...someone with more audio experience can likely add more information about this. I think they are called a radio "choke", and control power to the speakers when the radio HU is turned on. Again, not sure if there is a left and a right, but it is worth checking.
As a last resort, I would pull the head unit and start doing coninuity testing from the unit to the speakers...
Hopefully others will offer some advice - stereos aren't something I have a lot of experience with!