Advice needed on low volume and hum out of amp.

I just purchased a demo c-j MF-5600, multichannel amp online, and after connecting it to my Denon receiver, which I am using as pre/pro. The sound I am getting is at low levels, even when I turn the volume up noticeably. I previously had my front left and right speakers connected to two small monoblocks (Marantz MA-500's), which are rated about the same as the c-j (125 wpc), and never had this problem. I also get a hum out of the speakers. I assumed this was a ground loop that I couldn't isolate, but when I put one of the monoblocks on top of the c-j and reconnected the speaker to it, leaving all the cables and everything else in place, the sound level went back up and the hum disappeared. All components are routed through a power line conditioner. I am currently trying to work this out with just the front right and left channels only. I know this is not alot to work with, but maybe someone has had similar problems. Any thoughts would be greatly appreciated.
Perhaps the CJ amp inverts the phase? This may be a long shot but I know that some of the CJ preamps invert the phase and so this amp may also. I don't know what a wired-backwards amp sounds like so I can't say for sure. I don't know either if you would damage anything by swapping them to see or not. Perhaps others know. Good luck. Arthur
Try plugging the CJ directly into the wall outlet that the conditioner is using.
Try using a cheater plug on the amplifier or preamp.
If your audio system is connected to your cable system disconnect it and see if the hum goes away. Otherwise simplify your system AMP, Speakers, Preamp, CD nothing else and disconnect any other cables attached to those pieces and keep adding until the humm identify's the component(try a cheater plug)
Good luck ground hums are a pain to resolve sometimes, I found one in my system coming from a crappy Monster Cable interconnect.... I tore my system apart, bought conditioners etc... it was a bad interconnect.
Thanks for the help. The cheater plug helped reduce the hum alot. I still had the other problem and heard a crackle I didn't like. My local dealer was very helpful. He let me bring in the Amp, and he agrees that htere may be a problem, so I'll have to probably contact CJ directly.
If your sound system is used also for home theater, disconnect the cable line from the television. If this works, then get a couple matching transformers and connect the wire ends together but keep the 2 leads separate. Then put it in series with your cable line to the television. You will also need a small cable line to do this. Give it a shot, it worked for me.