i dont know a lot about this so I need some help. What is the difference between the klipsch gmx 2.1 and thx 2.1 speakers? and which ones are better

or should I buy the logitech z2200's?

I believe the main difference is the subwoofer output is greater on the thx 2.1 and better quality drivers in the sattelites. The gmx are a stylish alternative and a newer model so that may explain why you may be finding them at similar prices.

Either choice would be an upgrade to the logitech z2200. I have an original set of promedia 4.1(5 or 6 years old) and they still rock- currently using them in my bedrooms AV system. You can ad a second set of the 2.1's down the road for surround sound- with 2 subs.