Don't have any real world experience with the ambx but when someone actually mentions them online they can only talk about the lights, not the speakers. They look good on paper, though.
They are just a 2.1 system. Are you going to be watching movies on the pc, or just music. A 5.1 system will be better if you are doing more than just music (including games).
I will assume that if you are talking about an extremeGamer+Logitech x-540 setup that your budget is significantly less than $10,000.00.
For a good system I would take a look at the G51's or better yet the z5500 from Logitech. Also take a look at the Asus Xonar (D2 preferred but the D1's aren't bad) and the Auxentech Prelude as alternative's to Creative. If you do more movies and music I would stay away from Creative and focus on the Xonar and Prelude but it sounds like you might be more into games so Creative might be a better option, especially if you are still using Windows XP and play older games.
Pauldo