I live in Utah where we have a relatively high number of polygamists, and they're all shit heads. My girlfriend works with a woman who was raised in a polygamist environment, and that lady went through some horrible trauma. Polyamory is the umbrella term that contains what you want, and it's best to stick to it so that modern polyamory isn't associated with groups like the FLDS or cunts like Warren Jeffs. Polyfidelity is more or less what my girlfriend and I practice with her other partner, so I totally understand the appeal. I'll say that I do wish multiple marriages were possible, since it's effectively what we want in the long run. We'll probably have to approximate it with some form of contract or corporation.