How to hook up sub?

I have my main speakers attached to 5 way binding posts on my amp with spades. I use two sets of amp posts, one for the tweet/mid and one for the bass. Can I also connect to one of these sets of posts to hook up a powered sub via banana plugs? Any difference in going with the set handling the upper or lower frequencies? Any issues of impedence etc? I do not want to use the sub's crossover but rather to keep the main speakers directly hooked to the amp.
Thanks
Joe