I've sold my rigs but I had multiple rigs with multiple 79xx cards with Xubuntu. That guide in OP didn't work for me. Here is what I used, all from root terminal, hope it helps (I was using 12.4 driver)...
Clean old installs:
/usr/share/ati/fglrx-uninstall.sh --force
apt-get remove --purge fglrx*
sync
reboot
Install new driver (use defaults when prompted):
wget http://www2.ati.com/drivers/linux/amd-driver-installer-12-4-x86.x86_64.run
chmod 755 amd-driver-installer-12-4-x86.x86_64.run
chmod +x amd-driver-installer-12-4-x86.x86_64.run
./amd-driver-installer-12-4-x86.x86_64.run
aticonfig -f --initial --adapter=all
sync
reboot
Check cgminer is seeing all the devices:
cd <cgminer directory>
export DISPLAY=:0
export GPU_USE_SYNC_OBJECTS=1
./cgminer --ndevs
I would also check top to make sure only one instance of cgminer is launching.