[chamkill]

 Brilliant, I've grabbed it

For ref, here is my remote.xml - works really well.  I have no idea why I didn't think of it myself!   Once again, many thanks.

Code:

<?xml version="1.0" encoding="UTF-8"?>
<keymap>
  <TVGuide>
    <remote>
      <forward>NextChannelGroup</forward>
      <reverse>PreviousChannelGroup</reverse>
    </remote>
  </TVGuide>
</keymap>

 It's note include in this skin ? It's just usefull for me with a mibox ! I can't Switch groups with my remonte :/   

No because it overrides default behaviour.  You need to find the location of your userdata folder (see userdata (wiki)).  Inside that there is a directory called keymaps.  Create a file called remote.xml in the keymaps directory with the contents I posted and restart Kodi.  Now the ff and rew keys will change the channel group but ONLY in the guide window.  Everywhere else they will work as ff and rew. 

 hi black eagle, i try your xml on my mibox but it doesn't work.
so i try this...but it doesn,t work too   can u help me with tihs ? thanks

<?xml version="1.0" encoding="UTF-8"?>
<keymap>
  <TVGuide>
    <remote>
      <right>NextChannelGroup</right>
      <left>PreviousChannelGroup</left>
    </remote>
  </TVGuide>
</keymap>

for more info, the mibox's remote is a bluetooth device and it looks like this