I don't think the mono amp for stereo speakers is a good idea either. Your positioning won't be what it could be with stereo. But you said they were midbass woofers. If you mean then they will be filtered to not play the upper frequences or the lower frequences, I would think that the positioning wouldn't be as important since the lower frequences aren't as directional as the higher ones. I would say just to try it and just be ready for it not to sound as good as you would like. I would say sell your amp and buy a four channel one. Or maybe even brige the 4 channel indash receiver to 2 channels to power either the front or rear channels.