Hmm, since no one posted here, I guess I'll do it, then.
I tried the cables on both my Intel mac mini, and my colleague's '09 mini.
The MacPac cable does work with both machines. The Power Y-Cable does not work on the '09 mini. So much so, that the original Power Button didn't turn on the mini with the Y-Cable connected...
And I had to tell him that nothing was wrong with his computer.
If you want to connect the MacPac and wait til november for your Y-cable, then that's cool. But right now, all you have is the MacPac cable, and that will work for you.