Using an external Samsung HD TV on thunderbolt port No automatic switch back of sound

I have my Samsung E5000 TV attached to one of the 5K mac thunderbolt ports using an TB to HDMI cable. Works fine with all HD content (audio and vis) although MAC screen looks rubbish if select mirror current display , it drops resolution below 1080 and i have to manually select mirror mac display as it seems to default to samsung. . But I can live with that. the issue is when I turn TV off (but leave connected on standby) the MAC thinks it is still connected and continues to mirror the setting of the TV on the 5K. I can select use as separate display in settings from the top toolbar and that flips the mac back to 5K mode. However sound also stays piped to HDMI. Thus even though TV is oin standby, I have No sound on the MAC. Trial and error I have found I can go into sound settings and it shows HDMI being used so I flip it manually back to internal speakers and voila sound controls and sound comes back. But Id like this to be automatic pleaee what am I doing wrong . Ideally both automatic but at least sound as its at least 4 or 5 slicks to switch from HDMI to internal. setting idea below.