Yes, SmX is the material. It was developed by a guy who goes by the handle SandmanX, thus SmX. It is an acoustically transparent material that he sold to the DIY crowd at AVS forum for a while. He has since developed it into a complete screen company and no longer sells to the DIY crowd. He has a tremendous thread over there in which he documents the testing of all sorts of different material (Guilford of Maine fabric, Dazion, big name AT screen material, etc). Eventually he settled on a Pfiefer product (used to make window blinds I believe). He had them make some changes to their product to come up with the SmX material. It is a pretty cool story if you have a long time to read through his thread. His home theater is spectacular and has since been featured in Audiovideo Interiors Magazine, so you may of seen it before.
The website:
http://www.smxscreen.com/
