first off if the constant and accessory wires are flipped hooking up power in reverse would do no damage at all you just wouldnt have any memory and would have to reprogram your settings everytime you turn it on. as for the speakers have you tried hooking a speaker up to the green and green w/black wires to see if it is a speaker output?
Indeed this is not like the newer units....
Here goes :
Orange : +12V
Red : Acc/ignition
Yellow : lighting terminal
Black : remain the same, ground
Blue : remote out
Green, green/black : front speaker
Gray, gray/black : front speaker
Green/red, black/green : rear speaker
Gray/red, black/grey : rear speaker