hmm...the white boxes are each wired to the speaker wires coming out of the deck. If you look on those wires, they should have small lettering with "front left +", "front left -", etc. If they don't, check the installation manual for the deck and see which color is what. Whichever box is wired to the ones that say "front" is your front speakers. And, the other is rear. Are both back speakers working now? I would reverse the RCAs and then see if the other speakers work. (do front into 8/5 and rear into 7/4). If this changes the non-working speakers, then I would suspect that one of the channels on the amp doesn't work. If the same speakers don't work, I would suspect that the white box wired to them is bad. That is the more likely situation since you have already changed amps.
Yeah I re-edited my post. Are you running an amp for the subs and a seperate amp for the speakers? And is that a factory deck?
hmmm...i think my knowledge is at its limits. I would have to actually be there to try some stuff out. I would just play with some settings to see what they do to narrow down the cause. I'm sorry I can't help you more than I am able to without being there.
So here is basically how it should be run (sub amp included here):
You need 2 rca splitters (like cord 4 but they should sell ones where both male ends are the same color and not one of each).
connect the splitters to the rear rca and then into 8/5 on speaker amp and 1/2 on sub amp (watch colors here to make sure the red on rear rca is hooked to red on both amps, regardless of colors on splitter).
connect front rca to 7/4.
Beyond that, just play with settings on the amp and see what happens. I hope I have at least helped a little bit!