Yeah, that's infinite baffle. Neither the SA 8 or SD2 8 will work well in infinite baffle. Here's a good quote I found that describes what you need to look for when choosing a driver for IB better than I can:
The SA 8 has way too low an Qts (.33), and a little too high an Fs (35hz). The SD2-8 has an acceptable Qts(.58), but way too high an Fs(45.2hz). You're going to want to find an 8 with an Qts of >.6, an Fs ~30-35hz, and a decent amount of excursion.
With infinite baffle, I highly recommend getting drivers with more cone area! a Single 8" is not going to be very loud at all. But if you must, than the Dayton RS HF 8" is what I'd recommend. A little low on the Qts(.5) side but with an Fs of 28Hz you shouldn't notice that. Be careful, though, it doesn't have all that much excursion(9mm), and cone area and excursion are the things you need for output in infinite baffle! http://www.parts-express.com/pe/showdetl.cfm?partnumber=295-456