First things first, DO NOT UNINSTALL xserver-xorg-video-ati. It's just not a good idea, even if you use FGLRX. If you already removed it, then you should reinstall it ASAP.
Next you should install FGLRX. I have not used crunchbang in a long time, so i'm not sure if they offer FGLRX drivers in some package. If you can find a package, try it first before doing the manual installation. If no package exists, or when installed does not support your card, you need to download the installer from the AMD drivers web page. Good installation instructions are very established online, remember crunchbang is Debian based.
When you have finished installing FGLRX, and have restarted your computer, verify they are installed correctly with this command.
my workstation output, looks like this...
display: :0 screen: 0
OpenGL vendor string: Advanced Micro Devices, Inc.
OpenGL renderer string: ATI Radeon HD 5670
OpenGL version string: 4.1.11251 Compatibility Profile Context
As long as yours says "Advanced Micro Devices, Inc." and not MESA, you should be in good shape.
You should also just test your opengl output, with this command.
If you are having trouble, comment and I'll help.