Problem with the AMP800

IT IS SUPPOSED to be straightforward but for now, I don't know what's wrong with the setup.
So I purchased the AMP800. I connected behind the AMP800 an "unbalanced" (one line on the connector) stereo L/R cable that I plugged a " balanced " 1/4 to 3.5mm cable to my cellphone plug (this is the source, the music from my cellphone). After that I connected in front of the AMP 800 (on channel A or 1) a "balanced" (2 lines on the connector) stereo 1/4 to 3.5mm adapter for my Bose headphones (the bose uses a 3.5mm plug). I tried so hard to figure out how to have a clean sound but nothing is working, the sounds is not clear nor high. When I pull a little bit the 1/4 to 3.5mm adapter, the sound is more stronger then when the adapter is fully pushed-in in the A or 1 jack hole. Do you have any solutions to the problem? Thank in advance :)!!