Advice

If you are using a TRS cable coming out of the mixers stereo outputs and connecting it directly to a TRS balanced connection on a speaker or amplifier, you are getting stereo cancellation. That is why your signal is so weak. 

To best utilize these outputs in this application, you will need a TRS to stereo Y cable. This will split the stereo left and right from the output into two discreet signals that can be brought into a stereo amplifier or powered speaker.