The iSub/ soundsticks set that I have certainly includes a separate power supply, but I'm afraid that I don't have the pinout details.
The sound is wonderful. There is a huge difference, for example, between what it pumps out and the sound native to my iMac G5. The iSub/Soundstick combo was also very noticeably better than the speaker system that came with the G4 Cube that preceded my iMac, and that was miles better than the iMac's also.
I do seem to recall having read somewhere that an iSub will not work with machines running anything after X.4. Mind you, I haven't tested this personally, as I have nothing here in the house running X.5, but I would be delighted to learn that I had read wrongly, as I'd like to keep the things going for a good while yet.
What I can tell you is that my system sounds great, and that for casual listening it would be well worth your taking the trouble to get it working.