I do not hear any music through my 10" M Audio Subs (M Audio Sound System)
If you know how to use a multimeter, you can test the amp this way:
-unhook the subs
-hook up a cheapie speaker you know for sure works to one of the channels
-unhook the audio inputs
-turn the amp on
-set your meter to VDC
-put the positive probe on the inside of the input connector, being sure you make contact with th inner contact
-take the negative probe and tap it on the outside of the connector
What you are doing is sending a low voltage (replicating an audio signal) into the amp audio circuit and allowing the amp to amplify it. If the amp makes the speaker pop each time you strike the probe, the amp is working.
You mentioned you need a 4 channel amplifier make the two, dual voice coil subs operate. The is not true and by hooking them up like that, there's a chance of damaging the subs. The reason is that the dual voice coils are interwoven and they have to get electrically identical signals or they fight against each other. The can mechanically fail, then, electrically fail, then even damage the amp too.