Yeah that will work. The voice coil will just have to be able to dissipate the difference in the power. For example if one channel is running at 100 watts and the other is running at 120 watts then the voice coil will just have to be able to dissipate that extra 20 watts of power through heat. If I remeber right that magma is a pretty beefy sub so it shouldnt have any problem handling the small difference in power. If there is only one gain the difference between the two channels will probably only be a few watts. Oh yeah you will not be getting as much power that way. If its around 200 watts rms or 100 x 2 thats probalby each channel at 2 ohms stereo. You will only be getting around 50 watts x 2 becuase it will be 4 ohms on each channel stereo.