I run the CD5443 in my vehicle with the hpf on ( only option is on) with my CDT HD-62cf's off a diamond d5600.4 and on my HU i can usually hit around 63-65/80 on my hu before I get distortion with my gains up pretty dang high. Like everyone else says go back through your ENTIRE steps of installation and check everythig out. Also if you had the most minute short of one of your speaker wires it could be shorting when a high current is passed though the filter (in other words check your wiring) do it on the rca's also.
One of the great adventures of car audio and the reason many people are on this forum is because they like to do things themselves. I would bet almost everyone on this site that has put in a couple stereos has ad to hunt down some sort of problem similar if not identical to your own. Everyone one is trying to help, but sooner or later your going to have to pucker up, grap the multimeter and fix it.
Or......you could just give up and take it to a shop that might know only slightly more then you.