Thanks for the picture!
I've got the SX1240, and very interested in Antec's filter, USB & Firewire ports in the front for the performance plus series.
I've got a solution for your filter config. I just bought a a/c filter from ace hardware today. Looks almost exactly like the one in the picture (the grid spacing is larger though). Using a "supported" filter is very handy because you can drill though the plastic and directed mount it. Use some imagination ... you can drill and tap your case, or attach it to the front lower bezel.
Hope this helps!