HDMI Sound output dissapearing after first use

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http://askubuntu.com – I have a media centre with a ATI Radeon HD graphics card using Ubuntu desktop with all updates current which works fine for video and will also work perfectly for sound. The problem is that it seems after the first time using the media centre to play something the next time I come back to use it the HDMI output device is missing within the sound devices list (it's always there and not being used when I turn on the media centre for the first time). A reboot remedies this and I can then play a film or music through the TV (which is hooked up to the sound system). I appreciate there are other (HowTos)