Have you tried this..
EDIT: made a quick correction. It appers the wiki is wrong

I will update as soon as possible.
ssh -X user@
password: live
sudo su
chmod uog+rw /dev/ati/card*
xauth merge /home/user/.Xauthority
export DISPLAY=:0
aticonfig --odgc --adapter=all
Thanks!!! Now it works!!!
user@linuxcoin:~$ sudo su
root@linuxcoin:/home/user# chmod uog+rw /dev/ati/card*
root@linuxcoin:/home/user# xauth merge /home/user/.Xauthority
xauth: file /root/.Xauthority does not exist
root@linuxcoin:/home/user# export DISPLAY=:0
root@linuxcoin:/home/user# aticonfig --odgc --adapter=all
Adapter 0 - AMD Radeon HD 6990
Core (MHz) Memory (MHz)
Current Clocks : 970 845
Current Peak : 970 845
Configurable Peak Range : [500-1200] [500-1500]
GPU load : 98%
Adapter 1 - AMD Radeon HD 6990
Core (MHz) Memory (MHz)
Current Clocks : 970 845
Current Peak : 970 845
Configurable Peak Range : [500-1200] [500-1500]
GPU load : 99%
root@linuxcoin:/home/user# atitweak -l
0. AMD Radeon HD 6990 (:0.0)
engine clock range is 125 - 1200MHz
memory clock range is 75 - 1500MHz
core voltage range is 0.9 - 1.175VDC
performance level 0: engine clock 250MHz, memory clock 150MHz, core voltage 0.9VDC
performance level 1: engine clock 500MHz, memory clock 500MHz, core voltage 1VDC
performance level 2: engine clock 970MHz, memory clock 845MHz, core voltage 1.175VDC
fan speed range: 0 - 100%, 800 - 6000 RPM
1. AMD Radeon HD 6990 (:0.1)
engine clock range is 125 - 1200MHz
memory clock range is 75 - 1500MHz
core voltage range is 0.9 - 1.175VDC
performance level 0: engine clock 250MHz, memory clock 150MHz, core voltage 0.9VDC
performance level 1: engine clock 500MHz, memory clock 500MHz, core voltage 1VDC
performance level 2: engine clock 970MHz, memory clock 845MHz, core voltage 1.175VDC
fan speed range: 0 - 100%, 0 - 6000 RPM