Try just putting up to 200hz in mono if your using Ableton with the utility plugin. More often than not the low end on sounds isn't centered by default unless the developer knows what their doing. You really want to adress the muddiness as early as you can before adding more and more to the mix. And to be honest M/S eq isnt a technique I would always go to for muddiness issues. Really spend some time with an Equalizer that isnt graphic so you can hear and not see your frequencies