So you took the rears out "because they are broken"? Just how "broken" are they and in what way?
And you have an aftermarket subwoofer and amp - ok, you obviously have customized things quite a bit, so no one can base their guess on a factory set-up.

And you didn't tell us if the sub/amp are working or not. (Edit, as I read it again, it sounds like the sub was still working - or is it that ONLY the sub worked, then even it quit? I'm unsure.)
You did not tell us what kind of head unit you have.
You have not told us if the head acts like it is powered up or not.
And you tell us you have no voltmeter, so you can't even check for power at the head or amps.
You did not make it clear, is the factory amp still there or is that aftermarket as well?

And you want someone to guess what is going on.