Canadian 2.5RS

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

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?