Can't use fglrx drivers for Radeon HD 7990

[Firadeoclus]

Ubuntu 14.04.2 LTS

I am trying to install/use fglrx drivers for AMD Radeon HD 7990.

1) Search and launch "Additional Drivers"
2a) Either select "Using Video driver for the AMD graphics accelerators from fglrx-updates (proprietary)"...
2b) ... or select "Using Video driver for the AMD graphics accelerators from fglrx (proprietary)"
3) Press "Apply Changes"
4) A progress bar appears for a short time, showing about 10% progress
5) After a second or two, the progress bar disappears, "Using X.Org X server -- AMD/ATI display driver wrapper from xserver-xorg-video-ati (open source, tested)" is again selected. No error message or other failure indication is visible.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: software-properties-gtk 0.92.37.3
ProcVersionSignature: Ubuntu 3.16.0-34.47~14.04.1-generic 3.16.7-ckt8
Uname: Linux 3.16.0-34-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.8
Architecture: amd64
CurrentDesktop: Unity
Date: Tue Apr 14 15:10:22 2015
ExecutablePath: /usr/bin/software-properties-gtk
InstallationDate: Installed on 2015-04-13 (0 days ago)
InstallationMedia: Ubuntu 14.04.2 LTS "Trusty Tahr" - Release amd64 (20150218.1)
InterpreterPath: /usr/bin/python3.4
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_GB:en
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: software-properties
UpgradeStatus: No upgrade log present (probably fresh install)