I'd be interested to hack up the factory rear speaker box for a pair of JL 6W0s to get some real bass in the car, but for those of you that are curious, I'm in the process of installing the Hertz Mille 3-way kit in my Boxster that uses a gorgeous ribbon midrange driver and 6 1/2" mid-bass drivers with a 1" supertweeter. Should be quite decent without a sub. Good low end extension down to about 40hz, albeit no slam. Incredible mids and highs however (for $3000 speakers they better be, dont ask how much they cost me
). Driving them off an Audison VRX 2x200 amp and Eclipse Nav head.
I understand that rear speakers can provide nice fill, however you lose any imaging you would have had once you add rear fill. Its a bit different in a convertible with the top down, but if you look at any competition audio installs in almost any car, they never use any rear speakers.
With regard to the Bose thing, if you talk to anyone who knows anything about audio, they will explain to you just how bad the Bose components really are. Better yet, ask Bose yourself for a spec sheet for any of their products. They wont give it to you, saying "well our technology is proprietary and we dont divulge our secrets to our competition bla di bla di bla." If they consider foam surrounded, paper cone full range drivers and minuscule power supplied amplifiers their "proprietary technology" we must all really be missing something. Even the cheapest professional companies will give you full specs sheets on their products, as they have nothing to hide. Is a Krell amp better than a Rotel? Absolutely, but Rotel is still perfectly willing to share test bench results with the public. I'm sorry, but Bose is simply a company that has made a fortune off good marketing while putting out an absolutely sub-par product.
Just my $.02
Patrick