The cornerstones of Polyamory are honesty, integrity, and concern for everyone involved in a relationship. This is not the path you're walking.
By jumping directly from the theoretical possibility of polyamory as a beneficial change in your marriage to a fait accompli covert sexual relationship, you have totally set poly aside in favor of a garden-variety extra-marital affair. That's the sandwich you've ordered, and you'll have a hard time sending it back to the kitchen and trading it for poly, especially if your husband has the serious communication issues you refer to in the other thread, and he's only recently opened up enough to tell you there are problems in your marriage that have been building up over the years.
Whichever way you go, buckle up; it's going to be a bumpy ride.