Sound Guru advice needed!!!

I work for a non-profit organization and our conference room is about 15' x 40' and when people aren't talking sound carries all right, but when a lot of people are talking some folks can't hear. We have a set of modular tables that are usually set up along the length of the room. We'd like to add a couple/three wireless mics to reinforce the audio - not necessarily to "blast" anything. There is a sound system set up with an amp and several ceiling mount speakers. There is one RCA plug input available. I have some ideas, but I'd like to hear from any of you who have more experience.

Help!!!