We no longer recommend dual 8" subs, the space is just too tight and the rear seats don't like to latch in the upright position.  In the identical enclosure, though, we like to place a set of four (4) Focal Polykevlar 5 3/8" subwoofers.  Man, low end extension like the Image dual 8" setup, with incredibly smooth output and some real presence, like a pair of larger drivers with some authority.  'Or go with the dual 11" Focal enclosure (vinyl wrapped or custom painted fiberglass to match your exterior!) for your car.  See the subwoofer enclosure page for details.  Either enclosure layout works in all 996 coupes, 1999-2004.  We have a different, floor based layout for the cabriolet, also shown on the sub enclosure page.  You give us a paint code, and we'll paint either the fiberglass rear coupe enclosure or the fiberglass rear floor subwoofers with shallow 8" subs.