Trying to use the Radeon 8790M on my Dell Latitude E6540 running Kubuntu 13.04 (Raring). This laptop also has an Intel adapter (for power saving). lspci gives:

$ lspci | grep VGA 

00:02.0 VGA compatible controller: Intel Corporation Haswell Integrated Graphics Controller (rev 06)

01:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Mars [Radeon HD 8790M]

Tried using the standard fglrx and fglrx-update and aticonfig results in (in a message box):

aticonfig: No supported adapters detected

Trying AMD's drivers always renders the same result:

Your graphics adaper is not supported by this driver. Installation will not proceed. 

There is no 3D acceleration, as evident by running glxgears:

$ glxgears 

X Error of failed request:  BadRequest (invalid request code or no such operation)

Major opcode of failed request:  153 (GLX)

Minor opcode of failed request:  19 (X_GLXQueryServerString)

Serial number of failed request:  12

Current serial number in output stream:  12

This may be an issue of the multi-adapter situation, but I'm not sure how to resolve this.