Air Conditioning - Return air advice

Any advice/info on the following would be much appericated.

I have built a closet, approximately 4' by 5' to house my new air handler unit (Goodman's) which will provide heat/cooling for my finished basement. This is a heat pump system with 8kw electric strip backup. The basement is all open plan apart from 1 room (theatre room) that has an 8" flex duct return that goes back to said closet. The theatre room also has its own supply and I have several other supply ducts throughout the basement area. My original intent was for the air handler to have a return plenum fabricated that it would sit on and connect to the theatre return along with a main return air cut into the wall of the closet. I have received a Goodman's Air Handler Stand and am now thinking why try and duct from the bottom of the AH unit to wall, why not just have the opening in the wall with the AH unit on the stand (if that makes sense) which I think would work. The only bit I am not sure of is the 8" return from the theatre room. If I simply terminate the duct in the closet, would air be pulled back through it or would the pull of air simply come via the 'hole' in the wall (main return) leaving the theatre room return doing nothing.....this is where I need HELP. :wall:

Do it that way. If it dont work you can close off the grill to that room "some" .So you get more out of the 8" pipe.