Originally Posted by
wraunch
I believe it's an equipment issue.
May I ask what you base that on?
Far too easy to blame the equipment when little attention has been paid to the building envelope. It's not all about just keeping the air cool and dry. Your surroundings need to be cool as well, or you won't feel comfortable.
Other pro responders here have already advised you to not proceed without a load calculation. I add my voice to that. Anyone who comes to your home and just "eyeballs" a guess for what you need is wasting your time, and can become an expensive mistake if you go with someone like that. Same for someone who says "oh let's just add a return here and throw a few supply registers around, everything will be cool!" No, it probably will not.
Since you intend a home theater for the addition, you need to step up the quality of those you bring in to consult on this project. Big time.
Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.