So I am looking into fiberglassing some pods to add a pair of 6.5 inch speakers to my front soundstage. I think they will just fit in the corners of the windshield and yes they will cover over those vents. But I am not too worried about that.
What concerns me is the airbags. I see high up on the A-pillar trim the word "airbag" and I presume that is where the curtain airbags come out of that cover the windshield. I have seen a single cutaway illustration of an e90 with all airbags deployed here:
http://www.e90post.com/forums/showthread.php?t=256
But it is not clear as to whether speaker pods on the dash will interfere with airbag deployment.
The pods will be removable and I just have to figure out how to secure them so they dont fly back in the event of being rear-ended.
Edit: Okay, I think this (see photo below) will be a better location. It will be in the way when I get in or out of the car, but I can get over that. I do not use that space much when moving my feet around so being to the outside in front of the seat will likely be best.