I'd vote to just make marriage a legal contract that anyone over age 18, or minors with guardian approval, can agree to. One man and ten women? Sure. Two women? Sure. Who cares?
But, honestly, I get confused if one person is polygamous in two different relationships. Let's say I have five wives. Can one of my wives marry someone else, too? If so, what is my relationship to that wife's children by the other dude? Am I still a step-father?
Hey, maybe polygamy is the answer to the single mother problem. Maybe guys would stick around if they could have three more women around - to help care for the baby, to help with bills even, and to, you know, spread the love a little. I don't think it would, but hey, why not give it a shot?