Canadian 2.5RS

So I just got my SAE-1200D in the mail and installed it. Im pretty sure I installed everything correctly. This is far from my first time wiring an amp. The issue I had was that I couldn't get any sound from the subs so I started trouble shooting. I had good power, ground and remote cause the little green light was coming on, I checked my wiring for the subs and everything checked out there so I figured the problem must be in the RCAs. I check the HU to make sure the subs were turned on and they were. I broke out a new set of RCAs and ran them unimpeded to the amp and still got nothing. Then i decided to move the connection from the INPUT to the OUTPUT and voila, I got movement in the subs. They dont sound quite right but that may be because i haven't sorted through the many settings. so WTF? why does my amp only work when i have the RCAs going from the sub out on the HU to the amp output? and why doesn't my input work?

Anyone? Is it me or are my INPUT and OUTPUT eff'ed?