It can also be that you have not calibrated the volume output level for each speaker in your AVR or HT Processor. These speakers (and possibly amps) will have different efficiency ratings, which can indicate that the McIntosh speakers are quieter than the Magicos.
But yes, I would highly recommend getting a matching center channel at a minimum. The surrounds do not necessarily need to be matching, but they do need to be close in timber and sonic signature. (of course matching surrounds would be best solution).