Yesterday I did stop by the A/C shop and we came to the final solution. It is not the best but not bad either. I told him I got equipment closet (the 3x2 closet in the picture) which is 10ft tall but I only use up to 7ft so I want the return on top of that.
The A/C vents gotta be in front of that return and flow air away from it. Return should always be behind of the vents.
Remember, this room got vaulted ceiling so not many places got enough room for A/C vents or return
***BTW, my next thing will be moving the sub location to be under the equipment cabinet since currently it is in the same wall with kitchen so I don't want all the dishes fell off the shelves when watching movies :-) Now need to find the way to not vibrate the DVD player in there