Adaptor to connect external speakers to TV and Cable Box

[tehx]

Hi so I have some external speakers which I have connected to my TV. When I play something like a movie on the cable tv box I still get the sound from the external speakers because the box passes the sound through the HDMI connected to the tv. But the problem is my TV doesn't seem to support Dolby Digital passthrough over HDMI so I can only get dolby digital when playing stuff on my TV. 

 

Is there some kind of adaptor which connects TV & Cable Box to speaker system using their own separate wires and when I change the input from paying stuff on my TV to playing it on the cablebox the sound source on the speakers will change. 

If anyone knows anything like this or anything which can help me solve my issue it would be appreciated 

[SPG]

you mean a receiver?

[tehx]

3 minutes ago, SPG said:

you mean a receiver?

Yeah