You can definitely use the factory subwoofer from the DSP system, but it won't have the sound that you are after, since it only contains 2 puny 5.5" or 6" speakers (BMW calls them subwoofers where those should be mids for the rest of the worlds). I am 99% sure that the DSP system comes with a separate amplifier for the subs, so you will need an amplifier to drive those subs if you decide to use them. Besides, the enclosure and the subs are sold as one unit for about $300 bucks...for that kind of money, you can get a much, much better 10" sub. On the other hand, if you can find a DSP sub with enclosure at a junk yard, you can definitely modify the enclosure to be used with an 8" woofer, which I've heard sounds very decent. So, that's why you don't see anyone putting that OEM DSP sub into their X as a mod...it's just not worth the effort.