How to improve my product photo shoot to look like Apple's Mac Pro product site?

I think there are two important things to keep in mind:

1. The main idea with low-key photography is that you want to underexpose the background so much that the camera reads it as black. It doesn't even matter if the background is black or gray or some other color -- if there's no light hitting it, it's gonna look completely black. You've got way too much light on the background -- you need to make the difference in illumination between the subject and the background much greater.

2. There's no reason to think that Apple's image came out of the camera that way. As long as you've got some kind of clear difference between subject and background, you easily change the background to whatever you want. This took me a few minutes in Gimp:

That's obviously a long way from the quality of Apple's image. Some of the issues can be resolved with more attention to detail during the shoot. For example, it looks like there's some dust on the subject, and while you can remove that in post it'd be easiest to just make sure it's impeccably clean in the first place. Experiment with the lights to accentuate the interesting details, like edges. Make sure you really nail the focus. Other issues are probably easiest to fix with an image editor, like turning the background completely black.