I can help you rule some things out.
It cannot be your remote wire or your amp would not come on. It could also not be your ground nor power wires to the amp.
Things it could be:
Even though you followed that wiring diagram, you DID realize it was all positives connected together and all negatives connected together?
Next, turn your low pass crossover to the highest value, or set it to "off" or "flat" Do the same in your head unit.
With a song playing, slowly turn your gain up. Do not turn it past 1/4 if you still don't hear anything at all.
Turn your subsonic to about 30-35 if you have a ported box and don't know what it's tuned to. If it's a sealed box turn it to "off".