This question is specific to the placement of the HVAC return. Most theaters I have seen on here have their return located under the soffit, rather than on the riser of the soffit. Is there a particular reason for this? I have the option to do either, but I would think that the best performance may be on the riser part of the soffit.
It's not uncommon for theaters here to have a powered inline fan in the return. I'm dealing with that issue in my theater now, I think the Black Cat Theater used inline fans in both the supply and return, and I believe Nick****achi's theater and Moggie's theater had similar issues, but I can't swear to it. Those are just a few that come to mind when I start thinking about inline fans.
At any rate, Shawn is correct (was there ever any doubt ), with no "powered" return you shouldn't have an issue if the return grill is the same size as the inlet, assuming the inlet is quiet and you have a balanced system.